Home Forums Hunting & Shooting Gunsmithing I'm stumped, any suggestions????

I'll try to make this as short as possible. I just ordered an 8 twist Shilen barrel, chambered it in my wildcat, the 284 diablo. I have been shooting it about 30 times a day for the past week trying to find a load that meets my standards. I have shot bullets ranging from 180-110gr. Everything under 140gr will group half Moa or better but everything above 150 gr I'm lucky to shoot a 6" group at 100yds.

Does anybody have a possible answer to what is going on here? I would think that the heavier bullets would shoot better in an 8 twist barrel. I did verify that it is in fact an 8 twist

Run the numbers and see what you get.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Thanks for the link but not sure how that is going to help me with my questions.
An 8 twist barrel in a 7mm should stabilize any 7mm bullet available including the big 200gr bullets. None of the bullets are keyholeing so they seem stable. Just dosnt make sence why any bullet over 150gr won't shoot.

I did run the numbers on almost every bullet I've shot up to and including the big 200gr wildcat Rbbt. It says everything is fully stable.

Heavier bullets won't always shoot better in a fast twist barrel, but they certainly shouldn't shoot that bad when the lighter bullets are bug holing.

Always check the basics, scope rings and mounts are secure, action bolts are secure, and the scope hasn't puked on you. If that is solid, then something might be out of square with the action. I had a mauser that would only shoot one load well and that was only 1 1/2" everything else seemed to open up to 4-6" When a smith squared up the action and rechambered the barrel it's worst groups were 1 1/2" and best were 1/2".

Everything is good to go. This is a full custom rifle. I have double checked everything multiple times. I could see there being something wrong if just one load shot good and the rest bad but it's like a light switch was flipped as soon as you hit 150gr mark. EVERYTHING and I mean everything under 150gr shoots great and everything over shoots more like a shotgun.
Just seems odd to me and is confusing me. I guess I'll just have to keep playing with it. Thanks for the advise everyone

Twist in buttoned rifles can vary along the length. Might be that the overall twist is 8" but not consistent and this is damaging the longer bullets jackets? Not easy to measure the variation without some sophisticated equipment. Have you talked to Shilen?

For whatever reason, your wildcat may be "inherently inaccurate" with heavy bullets. Hopefully the answer lies elsewhere. Good luck and let us know what transpires.

I've never seen a rifle that is fundamentally solid shoot shotgun groups. A solid well built rifle shoots pretty much everything under 2" and bug holes the loads it prefers.

If it's not lack of twist making the bullets unstable, something is wrong and you're going to need to track it down.

I kinda leaning toward that the 284 Diablo just dosnt like heavy bullets. The rifle is sound and well put together. I can literally pick any bullet under 150gr with any appropriate powder and it will and does shoot consistently half Moa and under. If the rifle itself had issue I would think that it would show no matter the ammo.

What is the 284 diablo built off? Specs? It might just not like heavy bullets like you stated. If it was a twist problem or barrel problem I doubt it would shoot 1/2moa with most bullets. How did you measure twist rate? What does shilen say?

I haven't talked with Shilen yet. I leave for a hunt in a couple days. I will call them when I get back.
I used a tight patch and rid to measure twist.
284 Diablo uses a 300 win mag as the parent case.

Gotcha. So it's a 7mm/300win variant of some kind! Sounds fun. I'd think it would like heavy bullets with that much capacity.

The targets indicate otherwise than the gun being sound and well put together. Either something is wrong with the barrel or the action. Targets don't lie.

Not trying to start a pissin match here just looking for advise

458, can you explain this target to me? Which was shot with problem gun 2 days ago at 120yds with 140gr nosler btips. This is the norm not just a one time group. I have shot groups like this with 5-6 different bullets both lead core and solid copper and 4 different powders. Again no offense but an "unsound" rifle would not be this consistent and easy to shoot 1/4" groups. Yes I can see your theory but at the same time have to disagree.



For the time being, I have to side with that the cartridge design just simply does not like heavy bullets. I appreciate all the input and this continues to be an interesting rifle. Thanks

On a side note I am considering rechambering this barrel to a proven cartridge just to test and make sure I'm not going crazy. This would verify if it is in fact the barrel or cartridge design

Leave it as is, load 140s, be happy, go forth and kill schit.

Craigster, do you have any experience with 140 btips on game? My main consern is are they explosive at high speeds? 3500 + fps in particular. I suppose that the 140 accubond would shot nearly the same if so.

They have worked fine in my 7x57AI @ 3000fps (+/-). Can't say what they would do @ 3500.

I'd be interested in the results if you set it back and rechambered it in say a 7mm Rem mag or 7mmwby or 7stw. Very interesting results so far!

There is nothing inherent in a 8 twist Shilen barrel chambered in 7x300W that would cause it to be inaccurate with bullets heavier than 140gr...some might prefer think it ideal.

Some heavier VLD bullets are harder to find a good load for in any caliber, but for long range you need the higher BC, so you might try some different designs that are less sensitive...old standards like 162 Amax, eld or Scenar or BTHP, Berger Hybrid, Sierra etc...try a different bullet.

Some powders too...the combinations are many...you might experiment a little more.

If you want to shoot 140s you might want to lean toward Accubonds or monos at that speed, though they leave a lot of BC on the table.

What is your freebore? If your able to shoot the 140's well and getting anywhere near the lands then the heavys must be seated deep or you have alot of jump with the light bullets. If your necking your brass down and seating the heavys past the neck shoulder junction you could have a donut problem in that area. Just some thoughts to check.