Lightweight .243 Winchester - Calling 98Z5V

[Hooch]

Hello,

I have a lightweight AR-10 build that is currently waiting for a rifle length gas 22" .243 barrel that Krieger had on-hand. I don't have the barrel in-hand yet so not sure of the gas port diameter, but it currently has a .936" journal. I originally built this as a .308 big game hunting/backpacking rifle a few years ago but had problems with two barrels in a row from the same manufacturer, the chambers appeared to be cut off-axis to the bore. There were severe accuracy and over-pressure problems, even with super light starting loads. I've gotten more into coyote hunting lately so a semi-auto high velocity 6mm makes more sense, and Krieger happened to have the .243 barrel on the shelf.

The current build is a 2A Armament Xanthos receiver set with 2A titanium hollow takedown pins, Hiperfire trigger, V7 titanium upper & lower parts, V7 tool steel bolt catch, V7 charging handle, V7 magnesium 15" handguard, Smoke Composites short pull carbon fiber butt stock (7" length), JL Billet titanium bolt carrier with JP high pressure bolt (11.9 oz. BCG weight I believe), Kynshot 2.5" hydraulic buffer (3.8 oz.), Tubbs flatwire AR-10 spring and Rainier Arms gas tube (not sure of the length, will measure eventually). Don't have a gas block yet since the Krieger barrel has a larger journal than the .308 barrels. I currently run a Griffin Armament Paladin .300 suppressor (fairly high back-pressure it seems). This rifle was built with no cost constraints in order to minimize weight, I hunt very steep terrain and every ounce literally hurts. This is the reason for the lightweight recoil system components (titanium bolt carrier, lightweight buffer and short pull 7" buffer tube).

I've read a little bit of 98Z5V's advice about gas and recoil systems and have concerns that were always in the back of my mind. The .308 was a rifle length gas 20" barrel .750" journal diameter (never measured the gas port Ø) and I always figured it was over-gassed due to the lightweight recoil system components coupled with the suppressor. Bolt velocity did seem very high and I had to close down the adjustable gas block quite a bit, and it never ran very well. It was pretty hard on brass too.

My questions are:

1. Will this rifle ever function properly with a lightweight bolt carrier and buffer? I believe my current reciprocating mass is about 8 oz. less than Stoner's design?
2. Is the Tubbs flatwire AR-10 spring a bad idea? Compared to a regular spring it supposedly applies more force at full lock-up when fully extended, and the force doesn't ramp up as much when fully compressed. I do have a red Sprinco spring on-hand that was in the .308 before I put the Tubbs spring in.
3. The Krieger barrel was already drilled at rifle length gas, but would the lightweight recoil components function if it was drilled at rifle length + 1", 2" or 3"? I see that Craddock Precision drills 22" .243 barrels at either rifle +2" or 3".
4. If I need a heaver buffer (5.4 oz.?) are there any on the market at the 2.5" length? So that I can still use my current butt stock.

Sorry for the novel. I'm travelling outside the US right now and won't have this rifle in-hand again until June or so, but I will post pictures once it's complete.

 

[Hooch]

Edit to question #2...it must be the orange Sprinco spring that I have on-hand.

I know there's a lot of pertinent information missing here since I don't have the rifle/components in front of me, but mainly trying to see if I'm screwed from the get-go with some of these components. I will submit to waterboarding once I have everything in front of me

[dpete]

This isn't an answer to any of your questions or a suggestion of any kind.  Just an observation.  You have by your own admission a LOT of lightweight parts going into that rifle, especially into the rear end.  What is the contour of the barrel?  A .936 gas journal might suggest the barrel is heading toward a heavy bull barrel.  A bull barrel out front, especially at 22" long, and all those lightweight parts in the rear, could make for one very nose heavy rifle.  You mentioned a suppressor.  That will add even more nose weight.

[Hooch]

Hello dpete,

Good question, it's Krieger's AR10/DPMS profile with the Ø.812" option at the forward section of the barrel. I also have them fluting it. Only reason I went with this is because they claim a 16 month + current lead time for AR barrels at the time that they stopped taking orders. Krieger and Bartlein aren't even accepting orders right now because of so much demand, and I want this rifle ready for this upcoming winter. The .308 barrel on it previously was a stupid lightweight pencil contour at like 31 ounces.

Long term once this barrel is burned up, I aim to build this rifle into either a 6BRA or 6 Creedmoor with my own reamer, dies etc. and it will be a lighter contour. Might stick with the .243 since those cartridges are iffy with feeding? The barrel will be 22" long and I will optimize the location and diameter of the gas port, matched up to the proper recoil system components etc. I'd rather stick with all the lightweight recoil components if possible and hoping you guys can advise.

[dpete]

I'm sure someone with the skill and knowledge to make suggestions will chime in eventually.  But the general motto for a large frame AR is "Don't complicate shiit with complicated shiit."

 

[sagebrush]

i built a .243 krieger heavy barrel bench gun for prairie dog hunting. also started with light weight jp bcg with high pressure bolt. long story short, bought a toolcraft bcg and used that carrier on the high pressure bolt. also put a 10 oz rifle buffer (xh rifle buffer from heavy buffers . com). that combination slowed bolt speed down to very acceptable. not hard on brass. was using rifle stock not carbine.

[Hooch]

Thanks for the input sagebrush. How do you like the .243 in the AR platform, it feeds well? I'm interested to mess around with 55 grain ballistic tips at 4,000 fps, should be a laser out to 300 yards.

It seems this barrel/rifle will be on the extreme end of overgassed, early bolt unlocking and high bolt speed if I stick with the lightweight recoil system. Regardless of the gas port diameter or use of an adjustable gas block? I assume the .243 is quite gassy in general, this barrel has 2" more dwell length than a 20" barrel with rifle gas, AND I'm running a suppressor.

All things considered it seems best that I source a full mass carrier and at least a standard weight buffer. I see that heavybuffers.com offers a 5.5 and 6.5 ounce option in the 2.5" carbine length that I have, I will probably go with the 6.5 with their spring unless advised otherwise.

I may eventually do a dwell length experiment with the lightweight BCG and buffer. At the end of this barrel's life I could drill/test with the gas port at 4 or 5 locations, say every inch starting at rifle length. Keep drilling out the hole Ø at each location until the rifle cycles properly. Naturally the gas port will need to be larger in Ø the further away it is from the chamber/closer it is to the muzzle, so there would be a limit (i.e. probably don't want a Ø.150" gas port). But maybe this 22" barrel with a rifle +4" gas system would be a sweet spot? Can't imagine early unlock would be a problem when there's no gas until 4" past a normal rifle length system, but maybe bolt speed would still be a problem?

I'm sure someone has done this before, and the only real benefit is a ~ 1/2 pound lighter rifle. So probably a crazy idea altogether but still interesting to me.

 

[sagebrush]

never had any feed problems even with the bolt moving too fast, it was hard on case rims. mine is a heavy barrel 24" w/.936 journel, rifle gas. use a jp adjustable gas block. only have ever used heavier bullets. have stuck with 75gr v-max just for the splat factor.

12 hours ago, Hooch said:

Thanks for the input sagebrush. How do you like the .243 in the AR platform, it feeds well? I'm interested to mess around with 55 grain ballistic tips at 4,000 fps, should be a laser out to 300 yards.

It seems this barrel/rifle will be on the extreme end of overgassed, early bolt unlocking and high bolt speed if I stick with the lightweight recoil system. Regardless of the gas port diameter or use of an adjustable gas block? I assume the .243 is quite gassy in general, this barrel has 2" more dwell length than a 20" barrel with rifle gas, AND I'm running a suppressor.

All things considered it seems best that I source a full mass carrier and at least a standard weight buffer. I see that heavybuffers.com offers a 5.5 and 6.5 ounce option in the 2.5" carbine length that I have, I will probably go with the 6.5 with their spring unless advised otherwise.

I may eventually do a dwell length experiment with the lightweight BCG and buffer. At the end of this barrel's life I could drill/test with the gas port at 4 or 5 locations, say every inch starting at rifle length. Keep drilling out the hole Ø at each location until the rifle cycles properly. Naturally the gas port will need to be larger in Ø the further away it is from the chamber/closer it is to the muzzle, so there would be a limit (i.e. probably don't want a Ø.150" gas port). But maybe this 22" barrel with a rifle +4" gas system would be a sweet spot? Can't imagine early unlock would be a problem when there's no gas until 4" past a normal rifle length system, but maybe bolt speed would still be a problem?

I'm sure someone has done this before, and the only real benefit is a ~ 1/2 pound lighter rifle. So probably a crazy idea altogether but still interesting to me.

 

 

Edited March 11, 2023 by sagebrush

[Hooch]

Good to hear about the feeding. This barrel's chamber is kinda odd and has zero freebore, the guy at Krieger was a little surprised. But it's basically what I was looking for. Should work well with the 55 and 68 grain boat tails I wanna mess with. Might try some 80 grain boat tails at some point as well. Really want the high velocity out to 300 yards tho.

[98Z5V]

I'll get into this one today, and get some observations up that will help. 

Bottom line up front - I don't think it's going to function successfully, right now, if it's just assembled and you took it out to shoot it.

I'll have more info in a little while, once I go over it all.  

[Hooch]

Hello 98Z5V, do you have any thoughts on this whole thing yet? Interested to hear!

Things worked out in my favor and I have the rifle and new barrel in my hands, need to source a gas block and load up some ammo and will be able to shoot it. Haven't ordered the full mass bolt carrier and buffer yet.

[dpete]

@Hooch In the bullet dept. I have an unused but opened box of 55 grain Barnes Varmint-aTor bullets for .243.  This is a box of 100 projectiles, not loaded bullets. If they interest you send me a PM and we can figure something out.

Edited March 24, 2023 by dpete

[98Z5V]

On 3/23/2023 at 11:03 PM, Hooch said:

Hello 98Z5V, do you have any thoughts on this whole thing yet? Interested to hear!

Things worked out in my favor and I have the rifle and new barrel in my hands, need to source a gas block and load up some ammo and will be able to shoot it. Haven't ordered the full mass bolt carrier and buffer yet.

Busy work week - complete shiit-show, actually, and a busy weekend.  I'll get into this with specifics, but I'm just trying to clear my head today, relax, and not think about much. 

I'll be back in here with numbers. 

[Hooch]

On 3/24/2023 at 9:17 AM, dpete said:

@Hooch In the bullet dept. I have an unused but opened box of 55 grain Barnes Varmint-aTor bullets for .243.  This is a box of 100 projectiles, not loaded bullets. If they interest you send me a PM and we can figure something out.

Thanks for the offer dpete but for now I will stick with the bullets I have on hand. I was able to source ~500 of two different Bart's Bullets 68 grain boat tails, excited to see how well this rifle shoots them. Here's a picture from last night, still needs a gas block but otherwise ready to go.

98Z5V, I will measure the gas port diameter later this morning.

[Hooch]

The gas port diameter is .093" (Ø.936" journal). 

[98Z5V]

6 hours ago, Hooch said:

The gas port diameter is .093" (Ø.936" journal). 

Alright, man - I'll get on the math and get something in here.