Jp Lo-mass System Question

[ap3]

I was shooting my AR witht he JP ultra light lo-mass operating system in about 25 degree temperature and was experiencing failures to feed. The gun had not been cleaned before this shooting, but only because it had been cleaned fairly recently. It also had a sufficient amount of oil. My question is has anyone ever experienced problems with this system in cold temperatures, or does it just mean the colder it is the more frequency of cleaning required?

[George]

If you have the full on LMOS with alloy carrier (not stainless carrier), you need to do a few things to keep it running in all conditions, all the time.

First off, never lube it with anything heavier than motor oil. If you will be shooting in temp extremes, use a multi-grade synthetic one that is designed for low and high temps (5-30).

Second, make sure the buffer and recoil spring are lubed lightly with a real light lithium grease to keep friction down there. This also helps reduce the "Sproing" sound in the stock a little.

Third, make sure the bolt and rings get a few drops of real light oil (I use Kroil) in the bolt carrier holes every 50-75 rounds. This keeps the rings from getting sticky and making the bolt unlock harder which will make it malf eventually. The alloy bolts get sticky gas rings faster than the steel ones.

Fourth, make sure the gas system is tuned properly. Turn it down until the rifle just won't lock back on a single round fired from a mag. Keep opening it back up until it reliably locks back on the last round. Then open it another half to three quarters of a turn. Some folks just run it wide open and this may also be what is needed in your case.

Fifth, make sure that mags aren't seating high enough to add friction to the underside of the bolt. This will slow it down and cause this type of malf whenever anything else is also helping to slow the bolt down some (read cold weather here). To get the mags to sit a little lower, remove the mag catch and stone a few thousandths of the topside. This will also help mags seat reliably without banging them into place and prevent the dreaded "One Shot & Drop".

That's what I do with mine and it runs all de' day long in any dang weather ;-)

[ap3]

Wow, great stuff George!

I had tuned the gas system in warmer temperatures, but had not thought about the mags creating drag. I also had not been oiling the rings every 50-75 rounds with a temperature sensitive oil. I really appreciate the feedback as I was worried I would be at a match during a cold snap and end up with a malfunctioning gun.

[hockeydadnu27]

Wow, great stuff George!

I had tuned the gas system in warmer temperatures, but had not thought about the mags creating drag. I also had not been oiling the rings every 50-75 rounds with a temperature sensitive oil. I really appreciate the feedback as I was worried I would be at a match during a cold snap and end up with a malfunctioning gun.

How many rounds have you shot with this low mass bolt??

I can only get 1500-2000 round per low mass bolt and then worn out. I have JP CTR-02 open rifle. I have switch to the stainless bolt and so far it works great. I worn out 2 bolts before switching to the the stainless low mass bolt. My best luck was with the RyDol lube that came with my JP rifle in all temp.

thanks

Louie

[George]

John Paul did say to me once that he only felt they were ever going to get 3-4k rounds max outa' the alloy bolt carriers. My first one ran almost 10k before I replaced it. The above routine is what got it to that age with absolute reliability.

I also used the JP lube until I ran out of it which is when I switched to synthetic motor oil. It seems to like motor oil just as well, if not better :-)

The first bolt carrier and bolt combo I had (gold anodized carrier) ran with the one piece spiral gas ring (McPherson style). I changed the ring 3 times before I replaced the bolt and carrier. It always felt like it was wore out even when new (bolt and rings just flopped back and forth with no resistance) but functioned perfectly all the time.

The new carrier I have is a black anodized one and came with a more standard style red anodized recoil buffer and spring system unlike the carbine style buffer, soft spring and spacer my first LMOS carrier ran with. I have about 1400 rounds on the new system right now and it seems to be just about the same as when it was new and just settled in with a hundred break-in rounds.

The new system uses a traditional 3 piece gas ring system and exhibits a lot of bolt stiction from the ring fit in the bolt carrier. This tells me that the rings are gonna' scrape the plating off the inside of the carrier a lot faster than the old carrier I had and only time will tell if I get similar mileage to the old one or the lower life others are reporting.

I find that the new bolt/carrier system gets sticky faster and it becomes a little harder to extract a round by hand after 60-75 rounds whereas the older system ran 100=125 rounds plus before it ever got tight on unlocking. The drops of Kroil in the bolt carrier holes every 50-60 rounds is designed to keep this tendency in check.

None of my standard carrier AR's using either type of ring set exhibit this stickiness, only the alloy LMOS in my CTR-02 upper.

[Religious Shooter]

You might want to also see if it's an ammo problem. The ammo you are using may have less ommph at 25 degrees and is not creating enough gas/recoil for the gun to function properly.

[ap3]

Hockeydadnu27,

I probably only have around 500 rounds through the bolt carrier, and it doesn’t show any wear marks That does beg the question of what does the carrier begin to look like as it approaches the end of its life and what can be do to extend its life. I don't mind having to replace it periodically because the recoil control is such a significant improvement.

George,

I am using a standard 3 ring set instead of the Mcfarland ring, and it does have a bit of resistance as you described.

Religious shooter,

As far as the ammo goes since I was using an adjustable gas block and low-mass system I was not downloading the powder in my ammo.

Anyone,

I don't know enough about metallurgy, but I wonder if you cryogenically treat the alloy carrier if it would last longer. Any thoughts?

[TonyH]

Al,

I shoot one of the low mass carriers & have for several years now. I have never had a malfunction due to the carrier, ammo, yes. They do need to stay wet & have your gas system set up for your load, as George & others have said. I clean mine before a match & use FP10 oil, nothing heavier, then check my zero before I shoot it in the match. Then I usually don't have to worry about it again, unless were in the desert or that dust bowl in Reno. I have probably close to 7000 rds through mine with some wear on the bottom of the carrier, but nothing that would indicate it's going to stop working anytime soon.

Hope this helps in some way!

Tony

[ap3]

Just to give an update:

I cleaned and oiled as discussed here using Tony's suggestion of FP-10 and the carrieir ran flawless. I also used one of my match mags that is tuned. As a precaution I used some 600 grit sandpaper and smoothed out the inside of the receiver in order to reduce friction, and the carrier does seem to glide better.

Thanks guys for all the feedback.

Albert

Edited March 3, 2006 by ap3

[MikeFoley]

Albert, glad you are back up and running. Are you going to TN at the end of the month?

My LMOS runs 100% and I have more than 3K rounds through it. I generally clean the bolt group more than the rest of the rifle, and I keep it swimming in Break Free. I always oil the holes in the carrier prior to a match. It has ran in temperatures in the teens recently. Mine exhibits no signs of wear on the carrier or reciever. The only wear point is where it glides over the hammer. Who would have thought that lubrication would extend the life of anything, I thought that was just a myth.

Mike

[ap3]

Hey Mike,

Yes, I'll be at the TN match. They always run a good match. Since this will be my first match using the lo-mass system I am kind of anxious it will run 100%. I usually have enough problems with shotguns, so I didn't want to add rifle to the list.

[George]

AP3, I hope it wasn't a JP CTR-02 alloy upper that you sandpapered out. This takes the anodizing off the aluminum and is not a recommended tactic.

[ap3]

AP3, I hope it wasn't a JP CTR-02 alloy upper that you sandpapered out. This takes the anodizing off the aluminum and is not a recommended tactic.

No, DPMS lo-pro upper (non aluminum)

[George]

No, DPMS lo-pro upper (non aluminum)

Kewl ;-)