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JP Low Mass vs Full Mass system


Alaskapopo
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Well I have had my JP for a little bit now and love it. I ordered it with the low mass system. Last week I shot my JP and my Noveske in the same match. Used the Noveske for Tac optics and the JP for open. Both have a SJC Titan Comp on them now. I love both guns the JP is more accurate. One thing though I am not so sure about the low mass system. I can not tell a real difference in recoil. There is a different feel but not enough of one to make me shoot faster or more accurately. I did have an issue with the low mass system on the JP in this match. At around the 200 round mark since the last cleaning I could not load rounds into the chamber from the magazine. I had to single load the chamber and let the bolt push the case the rest of the way into the chamber. It fired fine but if I would have had to reload I would have been scewed. For me I think at this point that the full mass system is the way to go. Perhaps I am not a good enough shooter to feel the difference in recoil that the low mass system offers but I don't like the reliabllity trade off or rather the need to clean the gun more often. Just my opinion.

Pat

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The JP has a tighter chamber, has nothing to do with the carrier mass.

Swap carriers and you would find the issue follows the barrel. I have consistently found the JP barrels need a shoulder bump past what a normal case gauge proofs. Get the JP case gauge and make your ammo to that spec and the reliability will improve.

The low mass carrier, to me, is significant. Speed doubles at 30 yards or so tell the story.

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I've never had a full mass system in my JP so thanks for the comparison. JP's VTAC rifle runs a full mass so there's some support there. Any chance ammo was a variable factor?

I am sure it is possible. I think Marco is right on the chamber size as it works fine when its clean and the issues came when the chamber got dirty. To confirm I will have to swap my full mass system from the Noveske into it and see how many rounds it can go before the issue shows up.

Here is a stage where the paper was at 50 yards. I was running the JP in open and the Noveske in Tac optics so just watch the rifle portion.

JP at around 20 seconds. I had a wobble start.

Noveske with full mass at 39 seconds. The Noveske only weighs 3 more ounches both rifles have the same comp both have 1-6 scopes.

Edited by Alaskapopo
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JP at around 23 seconds

Noveske at around 18 seconds.

I like both guns. I think the perfect set up for me would be a full mass in the JP. I also will be replacing the Noveske barrel with a JP one when things get back to normal. The JP's barrel does shoot faster (150fps on average) compared to the Noveske and more accurate by about 1/3 to 1/2 moa depending on the load.

Pat

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Here is my friend who is a better shooter than me shooting both rifles as well. I asked him to shoot my rifles for me to give me an oppinion on the recoil characteristics of both systems.

Noveske

th_025_zpsd7a98b78.jpg

JP

th_022_zps4ac64c66.jpg

Edited by Alaskapopo
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The JP has a tighter chamber, has nothing to do with the carrier mass.

Swap carriers and you would find the issue follows the barrel. I have consistently found the JP barrels need a shoulder bump past what a normal case gauge proofs. Get the JP case gauge and make your ammo to that spec and the reliability will improve.

The low mass carrier, to me, is significant. Speed doubles at 30 yards or so tell the story.

With respect I think your half right. A tighter chamber will make it harder to chamber rounds as it gets dirty. But a heavier carrier and buffer will have more force to impart in chambering those rounds.

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With respect I think your half right. A tighter chamber will make it harder to chamber rounds as it gets dirty. But a heavier carrier and buffer will have more force to impart in chambering those rounds.

The energy is all stored in the spring and is exactly the same regardless of weight attached on the end. The lighter carrier will accelerate faster, the heavier one slower, and so the impulses are different, but the energy release is exactly the same.

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With respect I think your half right. A tighter chamber will make it harder to chamber rounds as it gets dirty. But a heavier carrier and buffer will have more force to impart in chambering those rounds.

The energy is all stored in the spring and is exactly the same regardless of weight attached on the end. The lighter carrier will accelerate faster, the heavier one slower, and so the impulses are different, but the energy release is exactly the same.

I am not sure if thats true. A large heavy hammer has more momentium than a small light one. Perhaps I am not understanding.

The gun cycled fine it was the initial loading that was the problem. At first dropping the bolt did the trick vs. running the charging handle. Later I had to put the rounds directly in the chamber and then let the bolt slam home. Anyway I still love the rifle a lot.

Pat

Edited by Alaskapopo
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Well that's the beautiful thing about AR15's... they can be whatever you want them to be. I always encourage people to try different things to see that works for them. The JP LMOS is very expensive and there are some, who prefer the feel and manors of a Milspec BCG. I agree with Jerry M. You should start with basic and change things only as you feel there is a need for change and an opportunity for improvement. I've had tremendous success with JP LMOS with exceptional reliability from my JP15. I've gone 1000rds between cleanings with only the occasional shot of oil to keep it all running and without feed failures. My JP has at least 5000rds down the stock barrel and I can count the number of failures on one hand. I like them so much, I just put a JP LMOS in my utility/bugout rifle. Every gun is different though and two rifles which look the same are not always the same in functionality. If a heavier carrier is needed for improved feed reliability, then the go for it, cuz the cost of a carrier is relatively low.

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is it possible the JP is under gassed? I use a full mass bolt/spring set-up in my duty rig and the low mass set up in my game rifle. I'm waiting on the new captured buffer system for the game set-up. I'm not the most diligent on cleaning either rifle.

I've never had an issue with the low mass set-up, but like the OP, I cannot detect a discernable advantage in the low mass set-up in my times.

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I have both the LMOS and standard weight BCG for my CTR-02. I prefer the recoil impulse of the standard carrier vs the LMOS. This is in part because I have other AR s for different applications that have standard carriers and they all feel the same to me. I did have to adjust my loader for the rounds to chamber in my JP as compared to my other ARs. I use a Redding small base sizing die and bump the shoulder a little more than standard. I use my JP case guage for random checks as I am loading and have not had any problem since I tweaked the loader.

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is it possible the JP is under gassed? I use a full mass bolt/spring set-up in my duty rig and the low mass set up in my game rifle. I'm waiting on the new captured buffer system for the game set-up. I'm not the most diligent on cleaning either rifle.

I've never had an issue with the low mass set-up, but like the OP, I cannot detect a discernable advantage in the low mass set-up in my times.

Not a gas issue as the gun cycles and locks back fine its the initial hand cycled round that is the problem when its dirty.

I will try to bump the shoulder back a tad on my ammo.

Edited by Alaskapopo
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I shot both of these rifles. I was shocked at the difference between to two. Both are very good setups but the clock doesn't lie, JP low mas for me, I just get faster shots. Talk about soft recoil, after the first two rounds I kept thinking the rifle was going to malf but never did. Its my first choice for competition but I wouldn't stake my life on it but that's what its for and I'm ok with that. The upper I'm building for this season has a JP low mass carrier.

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Man I have never had that problem. I will let my iron sight J.P. go for 7-800 round without cleaning and have never had this problem., but every rifle is different. I think your on the right track to bump the shoulder a thou. Or two.. Something to think about is that a tight chamber really doesn't get very dirty as it is much faster to seal, but it WILL be more susceptible to oversized ammo.

As for the difference in full weight to low weight, I notice the difference much more when I use a relaxed grip on the fore end. If you are real dynamic on holding the fore end, you wont notice much of a change, but if you loosen up and just let the rifle rest in your support hand you will se a huge difference and vast improvement.

Edited by kurtm
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I think the solution is to just have Ken shoot for you. If you can't tell a difference in recoil, then I would go with the full mass for reliability. Then revisit the issue from time to time as you improve. Who knows 6 months from now you might be able to tell a difference in recoil.

Travis

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