Has anybody tried a 7mm MOD?
I have not seen anybody mention the 7mm (about .284 cal), has anybody built one of those? Either for an Airforce type gun or any other plattform.
What rate of twist would you need in a barrel?
What would a good groove and land diameter for an airgun?
Would a powder burner barrel work after lapping down the lands?
I just think that it would be a good “in-between” caliber (.25 & .308) 😕
What do you guys think?
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UUPS!
You are total correct Walt! Guess the Swine Flu attacks the brain too! (Kidding)
How about a 9″ twist?
Picudo, you forgot to take your smart pill today. That is a SLOWER twist rate and will make the problems I had even worse.
walt
So you guys think that a faster twist would stabilize the bullet better?
There is an LW barrel with a 12″ twist, would that work?
How about the lenght of the barrel? 26″ – 28″?
that is correct, 1 in 9 1/2 inches twist.
And I thought you did it deliberately as a way of expressing your displeasure at the inadequate barrel/expense. 😆
crap, looks like the system interpreted the alpha string as an emoticon 🙁
that is correct, 1 in 9 1/2 inches twist.
Yes, but without the spaces so it shows as an emoticon giving people the finger on most peoples computers.
Isn’t that what I wrote?
Thats 1 : 9.5 😉
I built one using an old TC contender barrel. I think twist was 1:9.5″ if I remember right. The twist rate was too slow and would not stablize bullets very well. I tried everything from 175g to about 120g, all had sporadic grouping. The 120g and 140g stuff was okay, but would have occasional flyers. Very expensive experiment.
walt
I built a 6.5 using a 6.5×55 Heym barrel, wich had a pretty fast twist 1/10 or something. Got around 260 m/s with 140grain pellets. Shot hard but not extremely accurate 3″ at 50 meters. Maybe if I would have had acces to shorter bullets and a calibrating die it would have shot a bit better.
This is what I used:
Regards,
Marc[/img]
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There are a couple formulas for calculating if a projectile will be stable at a given twist rate, but after trying them out, I’m not convinced. There is only one way to tell, in my opinion, and that is to try it. But my barrel was a 9.5″ twist, so I would not anticipate you would have much improvement with a 9″ twist.
You can order custom barrels made with ultra fast twist rates; I have one in .308 with a 6.5″ twist, but it gets very expensive very quickly when you talk custom equipment. I think I paid $300 just for the barrel blank. So if it’s just a ‘hmmm I wonder…” type of curiousity’s sake experiment, most people aren’t fanatical enough to sink a whole lot of cash into such a project just to satisfy their curiosity. Of course, I have done a few of these myself, but only a few times. I don’t have the time or money to investigate each and every idea, so I try to pick the ones wtih the most promise. If you want to try them out, use barrels and calibers where there are lots of guns available, that way it is easy to find cheap surplus barrels for your experiments. Remington barrels are cheapest, I’ve found new take offs for $10 and other gunsmith friends have given me free ones. But as a general rule you get what you pay for. Remington barrels are some of the industry’s roughest cut barrels. They can still be very accurate; just rough on the inside.
walt