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Light recoil springs in an open gun


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I have 2 open guns that have the same problem in that neither will function with light recoil springs. By light I mean anything under 10-11 lbs.

If I use a lighter spring, 7-9 lb, I often get a feeding jam where the slide will stop with a few mm to go.

I can hand feed rounds through each gun with no problems. If I press down on the end of the compensator, hand feeding will be halted.

My theory is that the downward pressure generated by the gas in the compensator is sufficient to slow down the slide return.

My reason for this query is to find a solution as I much prefer the feel of the lighter springs. Strong recoil springs hammer me and result in very poor performance by the end of the day.

My guns have STI frames, Caspian slides lightened to 300 grams, Nowlin barrels with EGW cone compensators with 3 vertical ports and 4 side ports.

I run 9 major ammunition with 128 grain cast bullets with Hitek coating. I use 9.5 grains of Lovex D37.1 powder which is similar to AA7.

I would appreciate any advice.

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Nothing to do with the Comp.  Most likely bullet and/or ramp related.  Could also be magazine related.  Have you ruled out the mags?

 

Have you tried FMJ RN or HP? What's your bullet OAL?  Also, the barrel manufacturers chamber tolerances to the SAAMI specs can be a little tighter or more generous.  If on the tighter side, small amount of debris can cause feeding issues.

 

I would first try a 124 gn FMJ bullet. I use 124 gn FMJ RN with 9.6gn of AA7 and OAL= 1.165. 

Edited by jwhittin
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What caliber is it?  Can you get factory ammunition (even Minor) to try?

 

Were these open guns built by a gunsmith specializing in Open guns?  Are they new?  Did they ever work with light springs?  There are some subtle interplays with the barrel and comp and timing, but these are probably not it if it's barely stopping. 

 

Can you push the slide closed the last bit easily when it stops?  Have you cleaned and checked the extractor lately?  Do your rounds 'plunk and spin' in the chamber?

 

 

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Caliber 9 major. Minor ammunition works.

Guns are not new but they always displayed this problem.

I can easily close the slide the few mm after it stops.

Extractor perfect and not too tight.

Hand feeding with a full stoke always works even with a full magazine of 28 rounds and a 6 lb recoil spring. This seems to me to remove the feed ramp, chamber, magazine and extractor from the equation.

The rounds plunk and spin.

The chamber has been reamed using a factory Saami spec Manson reamer. Similar for the freebore.

Magazines are new MBX and STI. Gunsmithing was done by myself.

 

Is there any mechanism to apply upward pressure to the front bottom of the comp so that the friction between the upper barrel and the inside of the slide during the forward stroke of the slide is minimised?

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An old-school trick is to have the comp lightly ride on the guide rod to take some weight off when it's out of battery.  That can reduce barrel tip and battering of the upper lugs.

 

You may want to revisit your link geometry as well.

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Where is the nose of the bullet striking the ramp? And is it consistent?  Should be no less than half and about 2/3rd the way up the ramp.  
 

 

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Interesting.    You said "Minor ammunition works."  What do you mean?  Does it feed properly and reliably with the lighter recoil springs?  If so, points to difference in ammo measurements.

 

You are losing recoil energy somewhere.   Longshot - does your recoil spring move freely on the guide rod?  

Edited by jwhittin
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I run a 9 lb. recoil spring in my backup 9 major gun, and a 6V when I shoot 132 PF minor.  My main 9 major gun runs a 10 lb. spring.  Both slide to frame fits are tight.

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Yeah, there's something going on, and probably to do with the barrel being pulled forward by the comp as it fires if the gun won't close by itself if its only a 'few mm' open (how many is that?  8? 6? 4? 2?)

 

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The Barrel Link may be too long which would cause the upper lugs to not fully disengage as the barrel drops down when the slide moves back. If the upper lugs and barrel link have been setup properly then there shouldn't be any upper lug unlocking friction if you put upward pressure on the barrel as it unlocks. You can easily replicate this by putting a wood dowel or squib rod in the barrel with the gun locked up. Apply downward pressure on the rod as you slowly move the slide back. The barrel should cleanly unlock and fully disengage from the slide lugs allowing the slide to continue to move rearward unhindered.

 

When this isn't setup right it usually manifest as peening or damaged Upper Barrel or Slide lugs on the leading edge of the lugs. Inspect the Barrel and Slide lugs to see if damage is evident.

 

Basically put, this "interference" in upper lug disengagement as the shot fires and slide starts to move back will dramatically slow down the slide velocity.

 

Another potential would be the Hammer, Firing Pin Stop, Main Spring, or Hammer Strut doing something funky which generates a crazy amount of resistance as the slide starts to cock the hammer back. I have seen some guns with too short of hammer strut cause all kinds of crazy issues because the tip of the strut is hitting the top cap of the main spring housing in random places causing binding sometimes and none other times. How hard it is for the slide to cock the hammer during cycling effects the overall slide velocity.

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BUT...... Two different guns having the EXACT SAME ISSUE usually = Human Induced problem. Such as your thumb(s) are jamming into the side of the slide as you shoot. This is easily verified by blacking out the side of the slide with a Sharpie Marker then shoot some drills and see if any marker is transferring to your thumb(s).

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8 minutes ago, CHA-LEE said:

BUT...... Two different guns having the EXACT SAME ISSUE usually = Human Induced problem. Such as your thumb(s) are jamming into the side of the slide as you shoot. This is easily verified by blacking out the side of the slide with a Sharpie Marker then shoot some drills and see if any marker is transferring to your thumb(s).

This,

It can't be overemphasized enough how much the human affects how a gun runs.

I have tested guns side by side with someone and been unable to generate the same malfunction they are getting with the only change being the person holding it. 

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8 hours ago, CHA-LEE said:

BUT...... Two different guns having the EXACT SAME ISSUE usually = Human Induced problem. Such as your thumb(s) are jamming into the side of the slide as you shoot. This is easily verified by blacking out the side of the slide with a Sharpie Marker then shoot some drills and see if any marker is transferring to your thumb(s).

I was doing this on my LO gun. On my Open gun the optic mount prevents it. I've shot Open so long I guess I developed a bad habit of riding the optic mount with my support hand thumb. I had to utilize a nitrofin to keep my thumb off the slide on my LO

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Thanks for the comments. I have ridiculously short thumbs that cannot touch the slide as I have a shield as part of my thumb shelf and I cannot touch the sllde with my strong hand thumb.

I will test the link dimensions again as I have friction when any force is applied downwards on the comp.

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I have machined an extension for the normal steel guide rod that is approx 5 mm longer than usual.

The OD of this extension was sizes to have the compensator supported after unlocking.

This combined with a light lubrication (CLP) worked for my first indoor test session.

I fired just under a hundred 9major rounds using a 7lb recoil and 17lb main spring with no failures.

Next will be a test on matches to ascertain durability.

Thanks for all of the suggestions.

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On 6/15/2024 at 4:40 AM, jim vaughan said:

I have machined an extension for the normal steel guide rod that is approx 5 mm longer than usual.

The OD of this extension was sizes to have the compensator supported after unlocking.

This combined with a light lubrication (CLP) worked for my first indoor test session.

I fired just under a hundred 9major rounds using a 7lb recoil and 17lb main spring with no failures.

Next will be a test on matches to ascertain durability.

Thanks for all of the suggestions.

 

Sounds promising. Do you have a picture of the extension?

 

Similar barrel fits in both guns?

They cycle easily without the recoil springs installed?

Any signs of barrel bump or abnormalities on the cone of the comp?

 

The parallel between both guns raises some questions about shared items like other have mentioned.

 

Edited by Cam73
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On 6/10/2024 at 8:41 AM, jim vaughan said:

My theory is that the downward pressure generated by the gas in the compensator is sufficient to slow down the slide return.

 

The pressure of gases in the barrel and/or comp are already at Zero by the time the barrel even begins to unlock on the opening stroke.  It has long-forgotten about those gases by the time the slide starts to return to battery.

 

I concur with others on the barrel fit and Link issue.  If the link is too long or the cut-outs for the Supported Chamber are not deep enough, the barrel will want to stay up in the slide and interfere with its travel in both directions.

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You don't really need the ring if the rod itself will carry the weight, but that'll work.  It's also noteworthy you are using a cone barrel.  Bull-barrels don't tend to show this as much since the front of the slide can contact easier and keep the barrel from tipping as much.

 

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