Blowback Trouble and more

[dtech99]

I have been getting a significant amount of powder blow back in my face and occasionally I see visible flash from the ejector port on a Taurus PT1911. I have been shooting a 185 gr LSWC bullet with light loads while using a 10 or 11 lb recoil spring and have more than 12,000 rounds through the gun. The springs get replaced every 3,000 rounds or so and the barrel looks fine. I am beginning to suspect that the ejector port is opening prematurely but not sure what measurements to make to confirm this. I did measure the lug engagement in the slide and it appears to around .025 which is less than my other 1911's. Accuracy has suffered significantly at about time as this began with 50 foot free hand groups changing from 4-5 inches up to 10-12 inches. I also notice the breach face and ejector port area seem to soot up more than my other guns.

One additional odd thing has happened 3 times recently. I have not been able to pull the slide back to rack a round into an empty chamber. I fire the gun until the mag is empty and goes into slide lock as normal. I gently close the slide and drop the hammer to holster an empty firearm. When I install a fresh mag to start another round of fire the slide will not pull back at all. It does not move the least amount even under heavy pressure of pushing the slide against a hard surface. I had to remove the bushing and rattle the barrel and FLGR to free it up. I have not been able to identify any witness marks that would help me understand what actually bound up. The slide to rail fit is very loose so I am certain it is not junk binding in the rails. I do not see any damaged parts or cracks. I do not know if this jam is related to the blow back issue above. Any thoughts or tips on how to trouble shoot these problems would be greatly appreciated.

[niemi24s]

At first glance, I see 3 things based on what you've said:

• The recoil spring is too light
• Lug engagement is about half of what it should be
• Linkdown timing is goofed up

Q#1: What modifications have been done on the gun?
Q#2: What size link is installed?
Q#3: Has linkdown timing been checked?
Q#4: What's your 185gn SWC load or it's muzzle velocity?

[dtech99]

That lug engagement was measured both with the gun assembled and using only the rail and barrel. Both results are the same at .025. The limiting factor is the barrel lug height of .025.

1) The only modification to the gun was reducing the OEM 16 lb spring to the 10 and 11 lb spring based on the light loads I am using. Brass is ejected 3 to 5 feet over my right shoulder. Any less powder and it will not maintain slide lock at 11 lb. All other parts are Taurus OEM.

2) The link is the original OEM and I have not attempted to measure it. Need to find the procedure.

3) Link down timing has not been checked. Need to find the procedure.

4) The load is 3.8 gr Winchester Super Target, WST. A popular load for PPC. Calculated velocity is 660 fps at 8240 psi.

[niemi24s]

Refer to Post #4 in this thread:http://forum.m1911.org/showthread.php?t=54984&highlight=measure+engagement . Is this how you measured the vertical engagement?

If not, how did you do it?

[dtech99]

Yes, that is exactly how I measured the vertical engagement. The out of battery measurement is .160 while the locked measurement is .135 giving me the .025 vertical engagement.

[log man]

Without a doubt this gun is opening early as the engagement is shy of adequate engagement and with as many rounds down the pipe I would love to see the condition of the upper lugs. The accuracy says the same thing, gun opening and the barrel is moving down at the chamber before the bullet is gone. I'd say the gun doesn't need repair, it needs a complete rebuild.

LOG

[niemi24s]

Rats! Was hoping you'd measured it wrong and your engagement was reallly OK, but.....

There's a small chance your barrel's not going up far enough because of the link. Remove the link from the barrel and compare its measurements to this: http://i129.photobucket.com/albums/p232/niemi24s/scan0003atxtc.jpgand report back.

There's also a small chance the barrel's made funny, so while the link's removed, put just the link pin back in and use your calipers to measure the distance from the top center of the barrel (in the chamber area) down to the bottom of the installed link pin. It should be about 0.928". What's yours measure?

For linkdown timing measurements, go to our Tech Issues section and click on the "Test The Timing Of Your 1911...." link. But don't do any of the frame alterations called for.

You mentioned a very loose slide to frame rail fit and occasional slide lockup in battery. What might be happening is when easing the slide forward, the barrel and slide lugs don't mesh and the barrel (not vertically engaged with the slide) is pushing the slide up (due to its loose fit) and binding it to the frame.

With the gun fully assembled and unloaded, see if you can duplicate this binding and then look into the front of the ejection port and see if the aft slide lug might be sitting on top of the barrel - instead of into the barrel's #1 lug recess.

Might be a good idea to do this last check first. It's quick - the others will take some time.

[niemi24s]

Hi Log Man:I'd say the gun doesn't need repair, it needs a complete rebuild.Kind of what I was thinking too, but how's a gun get like this after only (only?) 12,000 rounds? Shot a lot in the dirt?

Cheers

[log man]

Hi Log Man:Kind of what I was thinking too, but how's a gun get like this after only (only?) 12,000 rounds? Shot a lot in the dirt?

Cheers
Well, he says the barrel lug height is .025" so it started that way.?

LOG

[niemi24s]

He said the 0.025" was the engagement.

[niemi24s]

Hi Dtech99: Just how much vertical play do you have between the slide & frame?

[log man]

He said the 0.025" was the engagement.

Okay, he did say that and he also said....

That lug engagement was measured both with the gun assembled and using only the rail and barrel. Both results are the same at .025. The limiting factor is the barrel lug height of .025.



Okay?

LOG

[niemi24s]

Hi Log Man:

Thanks for highlighting that in red for me. Missed it completely. In one eye & out the other. Gotta sign up for remedial reading - get a little more literate. You must have wondered "What in the world is he asking all that other stuff for?"

Wonder if the barrel lugs are only 0.025" high because of shallow cut recesses or because the top of the barrel is too thin? [Or did he say why and I missed that too?]

Cheers

[dtech99]

Let me see if I can get back in sync with the discussion. The vertical engagement and the barrel lug height are both .025 as stated. This is the original barrel and clearly the way is was manufactured. But I am not sure I can tell if it was a shallow cut or a thin barrel? The depth of the lug cut in the slide is about .060. The load bearing edge of the lugs on the barrel and in the slide show a very slight radius of the machined edge. The opposite side is the sharp squared off machined edge. I assume this slight radius is normal wear from locking and unlocking interference. I do not believe the link is limiting the travel of the barrel since I measure the same .025 engagement when the gun is disassembled and I measure the engagement using only the slide and barrel.

The vertical play between the slide and the frame measures .005 to .006. I understand what you are describing as the possible cause of the slide binding when the lugs do not mesh and the barrel lug could bind to the uncut slide roof. However, I have not been able to reproduce this binding to confirm that condition.

Thanks for all the help!

[log man]

Something to investigate is how early can it unlock, at what point of the slides rearward travel can you separate the slide from the barrel. To test and get an idea, push the barrel muzzle against a solid object and attempt to pull the slide back when the barrel is pushed back just a little .100" or so. It must of course unlock at .250" and have clearance, but it shouldn't at say .100" or less. There is no doubt that it is doing it. So it's redundant, but just for fun. As I said I do not believe there is a repair as the barrel lug recesses are shallow and should be at least .040" with .045"-.047"being more what match barrels will have. When you fire the gun the natural thing for the barrel and slide to do is pull in the opposite direction and with the corners rounding it is not going to take much barrel drop for it to do so and has been doing so.

LOG

[niemi24s]

As you can tell from Posts 12 & 13 I totally missed your statement about the 0.025" barrel lugs. The barrel got made funny - but not the way I implied in Post 7. Ordnance barrel lug height is about 0.060", #1 slide lug is about 0.061".

The slide/frame vertical play is about 0.002" more than the average mid-spec Gov't Model 1911 of 0.004", but what you have isn't really awful.

The slight radius at the corners of the slide & barrel lugs is there mostly because it's put there at the factory to ease engagement. The Ordnance spec is 0.005 to 0.010 inch radius for the barrel and 0.010 to 0.015 inch radius for the slide. Some is also no doubt due to wear.

As a minimum, I'd say this gun needs a new barrel and proper size link. The goal should be a minimum of 0.040" of vertical lug engagement when in battery.

Don't shoot any full power stuff in it until the vertical engagement is increased. Unfixable slide lug damage could occur.

Regards

[1911Tuner]

Did this just start happening recently...or has it always been a problem?

If it just started:

Look at the left side of the slide at the top of the port, about 1/8th inch forward of the corner. Look closely to see if there's a vertical crack that runs about a quarter-inch down, starting at the top of the port. You may have to look really close under a good light.

[dtech99]

niemi
I have not yet removed the link to make the measurements you recommended or performed the link down timing measurement. That will have to wait until next week as I will be busy with a pistol match over the several days.

LOG, per your post #15
The slide travels 0.175 rearward to produce 0.025 drop in the barrel at the edge of the port, unlocked.

Tuner
The blow back and occasional visible flash from the ejection port (1 out of 10 shots) has been there right along. At least as long as I have been using a reduced power loads with the lighter recoil springs. Lighter loads were introduced after the first 500 rounds of break in. Those unexplained slide jams while in battery on an empty chamber occurred within the last 500 rounds. The larger groups is also recent but that could be me? My wife shot a course of fire with this gun last night and scored much higher than me but well below her average using her Springfield. But she complained big time about the powder blow back in her face.

Close examination of the slide under a lighted magnifier did not reveal any cracks. I also wetted the surface with mineral spirits and watched it evaporate to see if it would highlight a possible crack. Nothing found.

[boehlertaught]

Is there a chance that the minimum engagment noted has resulted in some peening of the lugs over the 12K rounds. I seems it would not take much peening damage at that engagement to let the barrel go out of engagement too fast... or to not let the barrel actually engage, now, as much as it did when the pistol was new???

[niemi24s]

Hi Dtech99: Here's a few things to consider trying which might reduce the amount of blowback (other than a new barrel).

• Use a stronger recoil spring. My NRA Bullseye wadcutter target load has about 3% less muzzle energy than yours and the gun runs fine with a 14 lb recoil spring and a small radius firing pin stop (FPS). I does have a reduced power mainspring, however.

• Fit a small radius FPS. This will make it more difficult for the slide to begin cocking the hammer and will effectfively retard the slides initial aftward acceleration.

• Use a standard 23lb mainspring. I'm guessing your gun has a light trigger, attained (at least partially) by using a mainspring less than 23lb. A lighter mainspring make it easier for the slide to cock the hammer (regardless of FPS radius).

The next time you've got the gun apart, carefully examine the aft vertical faces of the slide locking lugs for evidence of "stepping". Assuming the slide has the usual 0.060" deep #1 lug , the barrel may have deformed the bottom 0.025" of them forward during the break in firings and less so after switching to the reduced loads.

If the slide lugs are stepped, they might eventually cause corresponding stepping in a new barrel with proper lug height.

Regards

[dtech99]

I removed the link to measure against the 278 spec provided and found several dimensions that fell out of tolerance. I don't know if they are significant to the problem.

The outside distance between the OD of the 2 holes is .4550 compared to .459 - .0015=.4575 min, under size
Center to center of the holes is .275 compared to .278 - .001=.277 min, under size
Inside distance between the holes is .0980 compared to .097 + .0015= .0985, in spec
hole clearance on the pin is .001 compared to .002- .001= .001, in spec
hole clearance on slidestop is .007 compared to .0055 + .0015= .007, in spec
pin hole OD is .1520 compared to .1570- .005= .1520, in spec
slide stop hole OD is .202 compared to .2050- .0005= .2045, under size
pin is .153 compared to.1550-.0005=.1545, under size
slide stop is .198 compared to .1995 -.001= .1985, under size

Distance between the top of the barrel and the bottom of the pin installed is .910 compared to .928, under size. This is consistent with the reduced engagement. However, if the barrel hood was .020 taller (or the lug .020 deeper) to gain more engagement the point of aim would be changed significantly . The gun has fixed front and rear sights which are very accurate for elevation.

I ran several hundred rounds using several main springs from 18# up to 23# in 1# increments. Also installed was a XP firing pin spring and an 11# recoil spring. In every case the primer strike fired the round and blowback/port flash remained an issue. Also during the passed several days as acting RSO for our match I observed well over 100 different 1911's which I never saw flash from the ejector port.

Examination of the lugs in the slide clearly show a witness mark from the barrel lugs at .025. I could not feel any step in the surface between the shiny and virgin finish. The witness mark was the removal of the parkerization at the lug engagement surface. Polished but no step.

[niemi24s]

I'd venture to say the link is a standard 278 link. The dimensions you gave seem within a thousandth or two of what they should be - and they're not easy to measure accurately. Most 278 links have no markings, but all the over or lundersized links I've ever seen do have markings stamped on them.

Your 0.910" measurement confirms the barrel out of spec in that regard also, but could be due to chamber area diameter or link pin hole problem. Deeper barrel lug recesses would change the POI, but taller lugs wouldn't (taller lugs would just fill the slide lug recesses better).

Good to hear the slide lug faces haven't been stepped forward. They should be ready to mate with a new barrel - when and if you decide to get one.

In the meantime, all that remains is trying a 14 or 16lb recoil spring in conjunction with a 23lb mainspring and a short radius FPS.

Regards

[dtech99]

I ran a test using an 18# main spring and a 23# main spring with my standard light load. Each main spring was tested with recoil springs 10#, 11#, 12#, 13#, #14 and 15#. I used the standard FPS as I do not have the short radius FPS. The firing pin spring remained constant using a Wolf XP FP spring. Starting with the 18# main spring I had reliable ignition, cycling, ejection and slide lock with the 10#, 11# recoil springs. Starting with the 12# spring the gun began occasional stove pipe and failure to slide lock. The condition got progressively worse as the recoil spring was incremented up to #15. Mags were loaded with 2 rounds during the test and each recoil spring was tested with at least 12 rounds or 6 mags of fire. Blow back was experience in each case but possibly decreasing as the recoil spring increased.

The test was repeated with the 23# main spring with similar results. Unreliable cycling and slide lock began with the 12# recoil spring. I also experienced blow back but it may have been reduced. A noticeable increase in trigger pull weight was present with the 23#.

While observing a second shooter with this gun I could see smoke blown rearward from the hammer/slide area. Using a second 1911 that fires very clean w.r.t. blow back and using the same light load I could not see any smoke blow back from the hammer area. Also after 100 rounds in the second 1911 the breach face and mag follow and mag side walls were very clean. The test gun had heavy soot on the breach, ejection port, hammer and the entire top 1 inch of the mags.

Based on the above results I was not able to draw any conclusion on blow back performance relative to the main spring or the recoil spring. Recoil spring performance was consistent with prior testing which I conclude that a 10# or 11# recoil spring was best for this load.

Much of this discussion has been directed to the barrel lock up and out of spec lugs. Could it be possible that the for some reason the case is not sealing in the chamber?

[niemi24s]

Could it be possible that the for some reason the case is not sealing in the chamber?Certainly. Either because of a low energy load or an oversized chamber.

See if your loads smoke up your face in another gun and either slug the chamber (or make a chamber casting).

There might also be the possibility excessive crimping is making it too hard for the case mouth to expand and seal the chamber upon firing.

What's your case OD right at the case mouth?

[dtech99]

I did test a second 1911 and did not see the rearward smoke and the chamber was very clean after 100 rounds of the same reload.

The barrel chamber measures .482
Reload crimp measures .470
Winchester factory round crimp measures .470
Spent reload case mouth and body diameter measure .477

[niemi24s]

I did test a second 1911 and did not see the rearward smoke and the chamber was very clean after 100 rounds of the same reload.I just caught that in your last post this a.m., so your ammo's OK in another gun.The barrel chamber measures .482The derived spec for that at the chamber face (aft end) is 0.480 + .002 inch, so that's OK. Don't see anything unusual in your other measurements either. Hmmmm....

The spec for the chamber ID up front at the stop shoulder is 0.474 + .002 inch, and that's where any blowby would originate.

What does yours measure?

[niemi24s]

Another thing to try is "crimping" your reloads just enough to straighten out any remaining case mouth flare/bell. The SAAMI max. case mouth OD is 0.473", so I'd suggest starting there, doing the "plunk test" and see if that'll help the case form a better seal with the chamber.

If your bullets are 0.452" and your brass has 0.010" thick case walls, you'll end up with a mouth OD of 0.472 to 0.473". The extra 2 or 3 thou might help your powder puff loads get the case mouth against the chamber wall. Maybe - as long as the chamber ID at the stop shoulder isn't too large.

[log man]

I don't really see the point with playing with the reloads when they shoot fine in other guns. The fact that this gun has way sub engagement seems to not be a concern, but I believe that is the problem , the wear and the tolerances are allowing the gun to simply open early. The second part of the original question in also an indication of a miss-fit as he said:
One additional odd thing has happened 3 times recently. I have not been able to pull the slide back to rack a round into an empty chamber. I fire the gun until the mag is empty and goes into slide lock as normal. I gently close the slide and drop the hammer to holster an empty firearm. When I install a fresh mag to start another round of fire the slide will not pull back at all. It does not move the least amount even under heavy pressure of pushing the slide against a hard surface. I had to remove the bushing and rattle the barrel and FLGR to free it up. I have not been able to identify any witness marks that would help me understand what actually bound up. The slide to rail fit is very loose so I am certain it is not junk binding in the rails. I do not see any damaged parts or cracks. I do not know if this jam is related to the blow back issue above. Any thoughts or tips on how to trouble shoot these problems would be greatly appreciated.
This sounds an awful lot like the upper lugs were not meshing and closed under the bind of the lugs against the slide and the link toggled closed like a pair of vice-grips, utilizing all the slop in the rails and bound up the gun.

LOG

[niemi24s]

Hi Log:

We have both told the OP the gun needs a new barrel but he seems reluctant to do so as it would throw off his sights (Post 21, para. 3)!

Even though his loads worked fine in the other gun, I thought maybe if the front part of his chamber was oversized (why not out of whack there too?), a little extra OD at the case mouth might help.

I've an uneasy feeling he'll just keep on shooting the gun as it is. Maybe he just needs better face protection from the blowback - or a nicer smelling gunpowder. :D

Cheers

[log man]

Hi Log:

We have both told the OP the gun needs a new barrel but he seems reluctant to do so as it would throw off his sights (Post 21, para. 3)!
Yeah, that is a good one as the group is 10"-12" and throwing that off would be a shame. Personally I would prefer a tighter group, 1"-2" and adjust the sights if actually needed. Just a thought.
Even though his loads worked fine in the other gun, I thought maybe if the front part of his chamber was oversized (why not out of whack there too?), a little extra OD at the case mouth might help.
The down side of a reloaded case at .473" is really no crimp and the resulting bullet push back.

I've an uneasy feeling he'll just keep on shooting the gun as it is. Maybe he just needs better face protection from the blowback - or a floral scented gunpowder. :D

Cheers
I think this is perhaps the truth. I remember as a kid playing with engines and guys trying to figure how to improve their smoky combustion when the cylinder was egg shaped and rings worn out. It's bore or bore and sleeve and new parts. And what this gun needs.....new parts.

LOG

[niemi24s]

Hi Log Man:The down side of a reloaded case at .473" is really no crimp and the resulting bullet push back.Well, you're in the majority. Most everybody believes crimping reduces bullet push (set) back. However...

...my semi-scientific tests have shown case grip is maximum (and set back is minimum) just after the bullet is seated. Furthermore, they've shown that anything done to the case mouth after the bullet is seated - even just knocking down any remaining flare/bell - will reduce case grip and increase set back.

But, that's another subject entirely.I remember as a kid playing with engines and guys trying to figure how to improve their smoky combustion when the cylinder was egg shaped and rings worn out. It's bore or bore and sleeve and new parts. And what this gun needs.....new parts.You mean there's no such thing as Motor Honey for the 1911? :D

Cheers

[log man]

Hi Log Man:Well, you're in the majority. Most everybody believes crimping reduces bullet push (set) back. However...

...my semi-scientific tests have shown case grip is maximum (and set back is minimum) just after the bullet is seated. Furthermore, they've shown that anything done to the case mouth after the bullet is seated - even just knocking down any remaining flare/bell - will reduce case grip and increase set back.
This may be very true, but I've not been able to chamber a belled case and if removing the bell loosens the cases grip on the bullet then the crimp will increase it.
But, that's another subject entirely.You mean there's no such thing as Motor Honey for the 1911? :D
Cheers
Not that I'm aware of, but that certainly means it's an open market. :)

LOG

[niemi24s]

Hi Log Man:. . . if removing the bell loosens the cases grip on the bullet then the crimp will increase it.That's what I thought too - up to a few years ago. The only amount of crimp I found which was better than no crimp at all was when the case mouth was buried about half way into the lead bullet with a resulting case mouth OD of about 0.465"! Any crimp less than that just increased setback.

If you get really bored, sniff around in these threads: http://forum.m1911.org/showthread.php?t=38223&highlight=bullet+setback+data and http://forum.m1911.org/showthread.php?t=38022&highlight=number .

Cheers