Author Topic: 257 airforce accuracy issues (Read 1722 times))

mrjohn357 · « **on:** June 30, 2019, 10:32:12 PM »

So, I’ve been trying to build an accurate 257 talondor having reading many threads for many years of Cedric, Doug/dyotat, knifemaker, bob, etc. i have a modified 25/257 dyotat valve, carbon sleeved (my doing) tj barrel from rjairgun supply (700mm but now has a 1/2 x20 threaded muzzle), solid bushings, swaged slugs, etc. and it still shoots like &^^&. Photo attached shows my handy work. Any expert thoughts on what is wrong? My hunch is my slugs are hitting the end cap but there are no signs ... i did make my own shroud but i left a lot of tolerance (no baffles, just hollow tube...have an “air stripper” without cone (could never make it accurate)), end cap diameter is .318 or so. Any recommendations (i can shoot a .25 cal just fine but maybe its me)

Desperate to get this money pit accurate.

Thx

mrjohn357 · « **Reply #1 on:** June 30, 2019, 10:33:57 PM »

Painfully, this is at 25 yards

screwwork · « **Reply #2 on:** June 30, 2019, 10:38:50 PM »

Take off the custom shroud and shoot a group maybe?

rintafile · « **Reply #3 on:** June 30, 2019, 10:57:42 PM »

Firelapped that barrel.

YEMX · « **Reply #4 on:** June 30, 2019, 11:15:46 PM »

Quote from: rintafile on June 30, 2019, 10:57:42 PM

Firelapped that barrel.

x2! Also, make sure your tank is tight. Don't over-tighten the fore end screw...

mrjohn357 · « **Reply #5 on:** June 30, 2019, 11:38:00 PM »

Thanks all for the fast response...i fire lapped the barrel, perhaps i need to do again (still have the wheeler kit)...without the shroud is the attached photo. Better, but not great (a vertical group). I am perplexed that the grouping would change that much.

Other facts: shooting off a bipod with a piece of cardboard under legs to allow slide on a hard table, tethered to 3200psi, slugs over sized barrel (.2565 barrel, slugs at .2567 curtesy of Noe sizing dies), photo with shroud is 10 shots, photo attached here is 5 shots

Seems like my homemade shroud is part of the problem but not all? Am open to experts saying i just need to work on my consistency....just dont know if thats it

KnifeMaker · « **Reply #6 on:** June 30, 2019, 11:54:30 PM »

RG, please tell me about the bullets. Particularly the length of the bullets, and the twist of the TJ's barrel. I'm guessing 1 in 14 twist.

Also, did you do a full re crown after the fire lapping? It is required after any lapping.

We'll get to the bottom of this! Yes, Yes We Will!!!

Knife

YEMX · « **Reply #7 on:** July 01, 2019, 12:35:37 AM »

Vertical stringing usually indicates breath control is a touch off. Left to right stringing is an indication of trigger finger position/squeeze issues. Perhaps you're still frustrated when shooting?

We WILL get to the bottom of the issue!!

mrjohn357 · « **Reply #8 on:** July 01, 2019, 01:24:58 AM »

Knife,

First, first time caller, long time fan. Have really appreciated your contribution to airgunning. Second, bullets are swaged using 4s nose, 80gr, with a boattail base. Not too different from nielson except he uses a 2s curve. Could try lightening up the gr but not sure thats the issue. Using Bob’s formulas (or someone elses..not sure) the bullet should be stable. Will get u the exact dimensions tmr.

The crowning and threading was actually done after the firelapping. Perhaps there is a shard that needs to be “relapped”.

YEMX,

appreciate the comment, definitely could be the issue but i dont see it when shooting .25 or .177 groups (although not slugs). Will try this week to redo with a focus on breathing

uncle paulie · « **Reply #9 on:** July 01, 2019, 07:26:10 AM »

Have you shot any strings over a crony? I'm guessing that last string is high to low...

pv

dyotat100 · « **Reply #10 on:** July 01, 2019, 10:40:45 AM »

Have you tried any cast bullets? A bullet that is know to shoot well?

I shoot Nick's stuff and there is a reason they are the size they are. That is what worked after testing. A 4 S nose is awful long. Sounds like there isn't enough engagement and the bullet needs to be longer. I would say over a 100 gr.

KnifeMaker · « **Reply #11 on:** July 01, 2019, 07:35:28 PM »

And remember, other than a boat tain which changes the twist needs, it isn't the weight, but the oal length that determines the twist needs.

Knife

Hobbyman2007 · « **Reply #12 on:** July 02, 2019, 05:14:40 PM »

As mentioned , first try bullets that are known to be good shooters in that cal from that barrel supplier . Eg: 257420 , 257388 , 257392( Noble) . Another thing to try is different bullet diameters . Just because some bullets shoot well at .2565” doesn’t mean they all do . I have two similar bullets that like to be sized .001” difference .

Love to see a pic of your bullets.

mrjohn357 · « **Reply #13 on:** July 03, 2019, 12:43:36 AM »

Thanks everyone,

I have a few of the molds that you have written about over the years (big fan, as I mentioned). I am gone for the next several days, will cast several types (Lyman, Noe, and arsenal). Its going to take a week or so, appreciate the interest and will post my results ASAP. Thank you.

mrjohn357 · « **Reply #14 on:** July 03, 2019, 01:02:57 AM »

Will also try a heavier gr (100 gr per Doug)...will try and figure out different sizing...as mentioned, slugged the barrel at .2565, sized at .2567...might need to order a few sizing dies from Al!

KnifeMaker · « **Reply #15 on:** July 03, 2019, 01:29:30 AM »

Sorry about the wierd spelleing of Boat Tails. LOL!

The sizing system from NOE is fantastic. I polish all of mine with a special High Rockwell Stainless Steel compound that Top Knife Makers use. It does not cut, but leaves a flawless mirror polish. It's called pure green chrome, and available from Custom Knife Making suppliers. I use Gun and Knife finishing supply company mostly.

I apply it to a shortened wooden medical grade cotton bud, and put it the Fordum. An industrial version of a Dremel.

Mike

dyotat100 · « **Reply #16 on:** July 03, 2019, 02:32:16 AM »

That is just a guess. Problem is the bullet will exceed the 1:14 barrel twist. I shoot the 2s bullets and I get under 1" group at 100 yds.

I have turned down my 257 to shoot 65 gr swaged at 950 fps. Gun is regulated at 2250 psi.

Jeremy1982 · « **Reply #17 on:** July 03, 2019, 10:15:23 PM »

Do you have a stock trigger?My set ups close to yours but made great improvements with the super sear 2 trigger set at 2 Lbs.Also with the bullets...mine likes the 80 gr NOE and Arsenal 85 splitzer at ranges out to 100 yards.On the close end range 60 yards or less the 63 gr NOE hp is a hands down best!!I get 5 shot .37 inch groups at 50 yards.Only other thing I can say to check is the o rings in the breech connector.I had a messed up o ring and my groups gotta crazy till I found it.

KnifeMaker · « **Reply #18 on:** July 05, 2019, 01:20:12 AM »

Quote from: dyotat100 on July 03, 2019, 02:32:16 AM

That is just a guess. Problem is the bullet will exceed the 1:14 barrel twist. I shoot the 2s bullets and I get under 1" group at 100 yds.

I have turned down my 257 to shoot 65 gr swaged at 950 fps. Gun is regulated at 2250 psi.

Doug, (Dyotat100) knows more abuot the twist and effects in the .257 than just about anyone out there.

Mike/Knife

darkcharisma · « **Reply #19 on:** July 05, 2019, 04:22:39 PM »

Doug, i would like to see your regulated plenum. Condor regulated is COOL

Thank you to our advertisers!

257 airforce accuracy issues

Author Topic: 257 airforce accuracy issues (Read 1722 times))