240xtp mag testing

[Nagantguy]

So to keep from being a huge initial post I’ll update each range trip.
Loadings consist of once fired Hornady brass. Federal small rifle primers. PSA lower. Bear Creek 16 inch upper
LillGun powder- yes I finally traded for a few pounds!
1. 240 xtp mag seated to the cannelure 36.5 lillgun. Crimped with LFCD .474-.475 at case mouth
No unburned powder- very moderate recoil . 25 and 50 yard accuracy was under one inch. Did not lock the action back
2. 37 grain little gun everything else the same. Accuracy at 25 yards was a almost touching 3 shot cluster slightly right of point of impact. No unburned powder did not lock action back.
3. 38 grains little gun- 3 rounds touching at 25, just about touching at 50! Did not lock action back.
4. 38.5 lillGun - outstanding 25 and 50 yard groups, maybe best ever for this rifle- recoil starting to feel like Hornady 250 FTX factory. Only down side action still not locking back.

Gonna try 39 39.5 and 40 next range trip . Hope accuracy holds until I find the sweet spot to ensure proper complete cycling of the action.
* all rounds fed and ejected just fine and put all brass to my right about 4 o’clock position but not as far away as FTX 250 factory or Federal fusion factory loads.

[s4s4u]

Do you know the size of the gas port?

[plant_one]

Do you know the size of the gas port?

i would be more looking to gas block alignment instead of port size.

that or a leak around the gas block. look for carbon tracks on the barrel under the handguard.

a leak might look something like this (pic from da web)


unlesss its dramatically undersized.. 38 grains of lil gun should be producing more than enough gas to get stuff moving properly for a BHO.




OP: did the gun lock the bolt with factory ammo?

[Nagantguy]

Yes sir the rifle locked back with both types of factory ammo .
I’ve seen no evidence of gas port leakage or misalignment.
I also figured that bolt would lock back at 38 grains little gun, and have yet to make a range trips with new rounds.
Hoot has loads listed as high as 40 grains so I’m creeping past 38 in .1 grain increments until I get the bolt to lock back.
Am I chasing an unnecessary goal, as all rounds thus far have fed and ejected fine and accuracy has been good?

[s4s4u]

I would punch a bigger hole and install an AGB so I could tune it for the lightest load that I would want to shoot. I don't shoot factory ammo so that would not be a concern, and I could always choke it down if it became necessary. Could probably lighten the buffer and get there as well.

[MOOSE EARS]

If it ain't broke, don't fix it! Locking open is no big deal, especially if everything's right otherwise. You're not in a life and death combat situation normally so using the charging handle is okay. Start opening up ports and messing around with buffer weights and you could cause problems. At this point, leave well enough alone and enjoy the accuracy and cycling as is. I have one that has done the same thing since being built. Who cares? Run with what you got and enjoy!

[plant_one]

I would punch a bigger hole and install an AGB so I could tune it for the lightest load that I would want to shoot. I don't shoot factory ammo so that would not be a concern, and I could always choke it down if it became necessary. Could probably lighten the buffer and get there as well.

you dont punch the gas port unless you absolutely have to. doing so "just because" isnt the right answer. you can easily create more problems than you have. going big just to put an AGB on there is the wrong answer, especially with a cartridge like this running the magnum pistol type powders. generally speaking BCA has these 450 uppers figured out.. so unless someone oopsied and grabbed the wrong bit (which is possible) the port size shouldnt be an issue. BCA may make budget uppers... but for the most part their stuff runs.

if it wasnt cycling correctly (full BHO Lock) with factory ammo - completely different story. i missed that part when i first asked about the gas leak. however sometimes things can shift too. ive had gas block set screws come loose on me and the block shift before and block a port partly.



what buffer/spring is a good question on the diag process at this point. without knowing that data point - we cant determine if more or less weight is likely to be beneficial. if its a completely unmodified PSA 6 position adjustable stock lower - that means its got a carbine (3oz) buffer in it and PROBABLY needs to have more weight and not less.


op:
have you tested again that the gun still BHO's with factory ammo?

also have you tested with a different magazine? (or do you only have one)

have you checked that the bolt catch isnt binding at all (maybe got some schmoo in there?)

or that the bolt catch is in spec? that rear tab on the bolt catch that the mag follower engages i've personally seen out of spec several times in my life. two LPK's i had (one a major brand name no less) and a buddy's both had the issue and had to be replaced to work with *all* mags. they would work with some, but not with others kind of thing. its a real easy part to machine the tip off of (or have it break off during machining i guess) and sneak past QC. doesnt take a lot to be out of spec with them and still have the function with some mags and not others based on follower design differences.

i'm wondering if for some reason the magazine isnt lifting the bolt catch, or if possible that the bolt carrier is outrunning the magazine spring lift on the bolt catch.

there's entirely possible a chance that with a light buffer (standard 3oz carbine) that your carrier speed is actually faster with the lil gun than with factory loads.


please give us a little more info on the firearm itself and we'll work through this. your load *should* be fine and cycling with full BHO. its probably something realtively minor thats stopping that right now.

[Nagantguy]

So yes the BHO works with both types of factory ammo, and yes it has a standard 3oz buffer and standard spring , I have 3 different magazines that have all run fine so far , bolt catch appeared to be working properly. I’ve yet to test my new loads and if I still have BHO failure My next step will be AGB. And or heavier buffer.

[s4s4u]

you dont punch the gas port unless you absolutely have to. doing so "just because" isnt the right answer. you can easily create more problems than you have

Anything you remove you can compensate for with the twist on a allen wrench. It is a great tuning tool and if you want to shoot less than full power loads and still have your gun function as it should it is something to consider. You do you. I do me.

[plant_one]

you dont punch the gas port unless you absolutely have to. doing so "just because" isnt the right answer. you can easily create more problems than you have

Anything you remove you can compensate for with the twist on a allen wrench. It is a great tuning tool and if you want to shoot less than full power loads and still have your gun function as it should it is something to consider. You do you. I do me.

look man.. i wasnt saying "dont do you"


i guess i should have been more specific that its not the correct first step to recommend to someone on the forums for someone diagnosing a reload cycling problem with a firearm that otherwise cycles with factory ammo.

as noted - there could still be multiple reasons why OP isnt getting BHO... and drilling the gas port may actually make the issue *WORSE*. yes i know.. adjustable gas block would correct that... but there you are compensating for possibly worsening a problem that was already a problem.

lets focus on finding out why its not functioning correctly and THEN suggest mods like gas port modifications.



dont get the cart before the horse and all that. and this below is exactly why.

So yes the BHO works with both types of factory ammo, and yes it has a standard 3oz buffer and standard spring , I have 3 different magazines that have all run fine so far , bolt catch appeared to be working properly. I’ve yet to test my new loads and if I still have BHO failure My next step will be AGB. And or heavier buffer.

go with at LEAST a h3 buffer if you can get your hands on one to test from another rifle, friend, etc. i bet you see that cycling problem go away. its a fair guess with that light of a buffer that your carrier speed is actually outrunning the bolt catch lift from the mag spring.

ie: it sounds like you're overgassed.

mind you... its right on the ragged edge, and factory ammo has just a little less gas, or a little different peak pressure curve than the LIL gun you're testing (because its not lil-gun) and thats why you get BHO with factory but even moderate charges of LilGun (your 36.5gr load) arent BHO for you.

most of us are running anywhere from 5-8oz buffers, or a combination of a lighter buffer and Hoots CCWS 4oz(ish) slug in the rear of our BCG's to get up around that range. I'm running that slug with a H3 (5.4oz) buffer... but i'm also running the 20" bushy upper thats carbine gas so YMMV. however at 9.5oz i'm still cycling just dandy. no issues with reloads or factory ammo.

Slash's buffers recommends that big bore AR's should have a 8.5oz buffer in them for proper cycling.



so give that a whirl, see where it gets you and please get back to us.