Help new build gas adjustment problem

[TitoR]

I just finished putting together a new build using the following:

Nordic 18" rifle length gas barrel

JP low mass bolt carrier + mil spec bolt

JP low mass buffer rifle

JP tuned buffer spring rifle

JP adjustable gas block

ARFX Rifle length stock

Noveske striped upper

AP customs handguard

Miculek comp

Rainier lower, JP trigger, a2 stock

I went to the range with a couple of boxes of different ammo (ultramax reman 55 grain FMJ, federal premium 69g match king, tulammo 55g FMJ) to adjust the gas system and sight in the scope. Followed instructions to adjust the gas block from JP, using Ultramax ammo, and was not able to make the bolt stay open with the mag catch even after opening the gas all the way (6 full turns). Repeated the process with the federal premium and different magazines with the same results.

I borrowed my brother's PWI BCG and was able to get the gas adjusted in a couple of shots, keeping the JP Spring and buffer. My brother's PWI rifle will work perfectly with the JP BCG, spring and buffer (16" barrel with mid length, non adjustable block).

My conclusion was that the combined mass of the JP BCG and buffer using JP's spring is to low, and can't create enough momentum to overcome the spring force. Ok, here are my questions

1. Does that make sense?

2. Does not make sense to me that JP's components are not playing well together. Is anyone running a similar setup? Have you experienced this problem?

3. Is the rifle length gas system underpowered to cycle the JP system?

4. Does Carbon Arms Nordic Barrel with the adjusted gas port cause this issue?

5. Any recommendations on how to make my setup run?

6. Will drilling the gas port in the barrel do anything to fix this?

There is limited I can do to swap parts due to the current industry crisis, so I NEED to make my setup work.

Thanks in advance.

[Sleepswithdogs]

The setup I run isn't all that different, and I have no problems. I don't think there is any problem with the JP parts not working together well, and I don't think you have come to the right conclusion as the lower mass of the JP parts would be driven rear even easier by the detonation of the round, not slower.

If it were mine, I'd be looking for a gas leak/gas block not seated correctly kind of problem. Drilling any gas ports is the very last resort, and there are many things to check and do prior to that.

There are a lot of very experienced AR people on here, and I'm sure they can get you dialed in.

Tar

Edited February 16, 2013 by Sleepswithdogs

[Heshin]

Just went through a similar situation with a similar build. http://www.brianenos.com/forums/index.php?showtopic=168184

If your buffer spring is the JP heavy spring I was told it has about 25% extra power and with the Nordic barrel it isn't necessary.

Sounds like you either have low gas or a resistance issue. Make sure your gas block is aligned over the barrel port and is wide open, your gas tube is aligned properly and that your gas key is not leaking.

[TitoR]

I triple verified the alignment of the gas block-barrel gas port, fit of gas tube, gas key and for any indication of gas leakage, and everything look ok. Like I said, just swapping the JP BCG to a full weight one allowed me to dial in the gas for perfect operation. So, increasing mass, with no other change, cured the cycling problem. What am I missing?

[Sleepswithdogs]

Not sure what's missing, because putting in a heavier BCG would require more gas, (you know, Newton and the opposite of "a body in motion," stuff) just as putting in a heavier buffer or stiffer spring would, and it sounds as if you have a low gas problem with your BCG. I'm thinking you may be check something and not realizing that it's incorrect. And it sounds like a leak in the bolt carrier group if you can swap it out and the rifle functions. If you live near Dallas, you are more than welcome to drop my JP LM BCG in to see how it runs.

[Heshin]

Try a mil spec buffer spring, if you have one. The lighter BCG may loose momentum too fast if your spring is too heavy.

Also if you swapped out your BCG for a full weight one without any other changes, your lightweight buffer added less resistance for that set up because of the higher BCG mass. If that makes sense..

[Vespid_Wasp]

Is this your first build? What kind of gas rings are you using on your bolt?

I think the first step you should take is swap out your buffer spring for a standard one. Drilling the gas port in the barrel should be your last resort.

[fastshooter03]

I just finished putting together a new build using the following:

Nordic 18" rifle length gas barrel

JP low mass bolt carrier + mil spec bolt

JP low mass buffer rifle

JP tuned buffer spring rifle

JP adjustable gas block

ARFX Rifle length stock

Noveske striped upper

AP customs handguard

Miculek comp

Rainier lower, JP trigger, a2 stock

I went to the range with a couple of boxes of different ammo (ultramax reman 55 grain FMJ, federal premium 69g match king, tulammo 55g FMJ) to adjust the gas system and sight in the scope. Followed instructions to adjust the gas block from JP, using Ultramax ammo, and was not able to make the bolt stay open with the mag catch even after opening the gas all the way (6 full turns). Repeated the process with the federal premium and different magazines with the same results.

I borrowed my brother's PWI BCG and was able to get the gas adjusted in a couple of shots, keeping the JP Spring and buffer. My brother's PWI rifle will work perfectly with the JP BCG, spring and buffer (16" barrel with mid length, non adjustable block).

My conclusion was that the combined mass of the JP BCG and buffer using JP's spring is to low, and can't create enough momentum to overcome the spring force. Ok, here are my questions

1. Does that make sense? Yes, too light on mass and the spring can overpower the system. Might not make sense but that's how it is. Been throught that....

2. Does not make sense to me that JP's components are not playing well together. Is anyone running a similar setup? Have you experienced this problem?

It says you're using a nordic barrel. I don't think JP uses nordic barrels?? Maybe I'm wrong. Heshin is right...this is the second thread about this lately..

3. Is the rifle length gas system underpowered to cycle the JP system? See question 1.... was size gas hole??? Higher quality rifling seems to have less port pressure IMO.

4. Does Carbon Arms Nordic Barrel with the adjusted gas port cause this issue? Bingo! BTW adjustable GB not needed for 18" rifle length.

5. Any recommendations on how to make my setup run? Lighter buffer spring, normal weight buffer or BCG.

6. Will drilling the gas port in the barrel do anything to fix this? Yes but might not be neccessary

There is limited I can do to swap parts due to the current industry crisis, so I NEED to make my setup work.

Thanks in advance.

See answers in red....

I REALLY LIKE using JP's BCG stuff but I always stick with the normal mass pcs.

Your Brothers midlength 16" should have more gas power than yours unless the gas hole is smaller...even then it still might?

I would try running a carbine spring or take an old spring and start cutting it down.

If you have a standard weight buffer I would try putting that in.

Wolff RP buffer springs are available but I would worry with all the Low mass parts in there about it closing properly. For $15 Brownells..worth a try.

Recoil tuning is a real balancing act for sure.

Last resort is to make the gas port bigger.

Nick

[TitoR]

Not sure what's missing, because putting in a heavier BCG would require more gas, (you know, Newton and the opposite of "a body in motion," stuff) just as putting in a heavier buffer or stiffer spring would, and it sounds as if you have a low gas problem with your BCG. I'm thinking you may be check something and not realizing that it's incorrect. And it sounds like a leak in the bolt carrier group if you can swap it out and the rifle functions. If you live near Dallas, you are more than welcome to drop my JP LM BCG in to see how it runs.

The problem I have is with a JP LM BCG. I would have thought that the mil-spec BCG needs more gas, but what i experienced is the opposite. I adjusted the gas block to run with the increased mass of the mil-spec BCG, but unlike with the JP LM BCG, which I opened the JP Adj Gb fully (6 full turns) and still the bolt did not stay open, the rifle would run perfectly with just 4 1/2 turns of the gas block with the mil-spec BCG. Thanks for the offer, but unfortunately I am in Puerto Rico.

[TitoR]

Try a mil spec buffer spring, if you have one. The lighter BCG may loose momentum too fast if your spring is too heavy.

Also if you swapped out your BCG for a full weight one without any other changes, your lightweight buffer added less resistance for that set up because of the higher BCG mass. If that makes sense..

I ordered a mil-spec buffer and buffer spring to run some tests, as I tend to agree with you. Probably will take a week for delivery.

[TitoR]

Is this your first build? What kind of gas rings are you using on your bolt?

I think the first step you should take is swap out your buffer spring for a standard one. Drilling the gas port in the barrel should be your last resort.

It's my first build and the bolt has three regular rings, staggered. I am waiting for a Brownells order with a standard spring and buffer to test the "too light" theory.

[Sleepswithdogs]

There are some really experienced builders on here. I have built a few, but have not run into many problems. You need someone like Pat or Co-Experts, MarkCo, one of those guys to help you with this one. As much as I would like to, I just don't have any more suggestions to offer. We were always taught that "diseases don't read text books," and weapon problems are similar. Sometimes things that don't make sense make problems.

Edited February 17, 2013 by Sleepswithdogs

[MarkCO]

You are dealing with a momentum issue. If you go with a standard buffer spring, that should fix the problem.

You might have some gas sealing issues with the bolt and this would cause the same symptom. There are some really bad bolts hitting the market lately. Gas tube seal to key is also a potential area of misalignment and leakage, but less likely since the other carrier worked. Try swapping bolts in the JP carrier and see what that does. Drilling out the gas port would be masking a problem, so not a great idea.

[Steve RA]

Only make one change at a time, changing several components at one time usually masks problem or even makes it worse.

[Heshin]

Only make one change at a time, changing several components at one time usually masks problem or even makes it worse.

This is a must!!

[doubleaay78]

Make sure your gas tube isn't upside down.

ETA never mind, saw that it works with a full mass bolt carrier.

Edited February 18, 2013 by doubleaay78

[TitoR]

You are dealing with a momentum issue. If you go with a standard buffer spring, that should fix the problem.

You might have some gas sealing issues with the bolt and this would cause the same symptom. There are some really bad bolts hitting the market lately. Gas tube seal to key is also a potential area of misalignment and leakage, but less likely since the other carrier worked. Try swapping bolts in the JP carrier and see what that does. Drilling out the gas port would be masking a problem, so not a great idea.

MarkCO, thanks for the advice. Several instance of people suggesting that the rifle needs more momentum (mass) or less resistance (spring). This how I am planning to proceed:

1. Re-check all gas connections: gas block to barrel gas port alignment, gas tube to gas block fit, gas tube to gas key fit, gas key tightness to carrier bolt, verify gas passage through gas key to carrier, and gas rings fit to carrier bolt.

2. Swap JP spring for mil spec buffer spring. Adjust gas and test. If it does not work, keep change and then,

3. Swap JP LMOS buffer for mil-spec buffer. Adjust gas and test. If does not work, keep change and then,

4. Swap my bolt for my brother's bolt. If does not work, revert all changes and then,

5. Star cutting mil-spec buffer spring 1 coil at a time.

I am out of ideas after 5 above. Anything else I should try?

BTW, is there a Loctite product that could be used to seal gas tube to gas block or the gas key to the carrier?

I'm waiting for an order from Brownells to start the troubleshooting again. I'll rout back on my findings, as it may help others.

[MarkCO]

BTW, is there a Loctite product that could be used to seal gas tube to gas block or the gas key to the carrier?

The second, yes. However I have never seen a JP carrier leak. Not that it is not possible, but unlikely.

If you have leaks at the gas block, you will see evidence of it in carbon sooting.

[TitoR]

MarkCO

Here is a photo of the gas tube at the gas block. Do you consider this carbon sooting abnormal?

Thanks

[MarkCO]

That amount looks typical for a JP block with maybe 1K or so rounds on it. But the pattern is asymetrical which is not real common.

[TitoR]

Ok, here is the latest range report. Changed the JP spring and buffer for mil spec units and was able to adjust the gas block 4 1/2 turns to run with the 69g Fed Premium ammo. Ran out of ammo, so tried the tulammo, but did not work even after fully opening the gas block.

Next, buy more ultramax ammo and run test again, but this time I am bringing my dremel to start cutting the spring.

Any recommendation on how much to cut at a time or the maximum before I start running into bolt closing issues or feeding issues?

[Heshin]

Are you still using the lmos Bcg? If so re install the jp lmos buffer with the mil spec spring. Light BCG, light buffer. Full weight bcg, full weight or lighter buffer.

[TitoR]

Are you still using the lmos Bcg? If so re install the jp lmos buffer with the mil spec spring. Light BCG, light buffer. Full weight bcg, full weight or lighter buffer.

Heshin, thanks for your reply.

I only have the JP LMOS BCG, so I'm stuck with it.

So, let me see if I understand. I still want to keep the overall mass low, even though the rifle is showing signs of undergasing which is causing short stroking? And on my test with the mil spec buffer and buffer spring, the real help was the spring and not the buffer? So, if I switch to a "softer" spring by either cutting coils from the mil spec spring or getting a carbine spring for my rifle length tube, it would allow the BCG/Buffer to move all the way back and stop with the magazine catch? BTW, is the carbine spring in a rifle tube a good substitute for cutting coils from a rifle length buffer spring for this issue? I hesitant to start cutting coils.

I did not try the JP LMOS BCG with the mil-spec spring and JP lightweight buffer, so I'll add it for my next range session. I'm also buying a carbine spring to use in the rifle length buffer tube, which I'm planning to test too.

BTW, I failed to mention that this is my first build and my first 3 gun rifle too, so I can use all the help you can provide. And, yes I am an engineer who likes to DIY.

[Heshin]

To me it sounds like you are fighting resistance somewhere if your gas system checks out, so changing to the mil spec spring and continuing to use the LMOS BCG AND LMOS Buffer should help. Also make sure you have plenty of lube on your bolt and BCG.

If you have done this and you are still having the same issues I would think that you have a gas problem somewhere, but there are much more experianced people here than I that will hopefully chime in after your test.

[TitoR]

Glad to report that the rifle finally worked with 55g ammo, specifically American eagle FMJ. The trick was the mil spec spring with the JP low mass buffer and BCG. But mostly, I believe it was a lubrication issue. I went to the range with the rifle dropping wet with CLP, and it ran with 55g with the same gas setting as the 69g fed premium, with the mil-spec buffer and spring. Still it won't cycle tulammo.

This was a limited test, still need to run several hundred rounds to break the rifle in, but now I can do it with full mags.

BTW, any recommendations on best lubricant for competition use?