December 11, 2014 at 7:38 pm #18321
I know its been a while but finally got out for a quick shooting session this past Monday with the Corsair+ 7mm.
BARREL/MOLD DRAMA: To this day, I have bought and installed a TJ barrel liner with 1-14″ and one with a 1-10″ twist. This first video I made on the completed gun was with the 14″ twist barrel. You can see the video here: https://www.youtube.com/watch?v=Lct_L6BtRdE&list=UUDBsDGN9infjfprvoHuqE6w The performance with the 14″ twist was really good and showed promise but at the time, i owned LESS than STELLAR bullet molds from LEE and I knew groups could be better. I also had a LBT mold on order while I tested the 14″ twist barrel. When I finally got the LBT mold, I discovered that the 14″ twist barrel was too big with a bore diameter of .2853″. And 7mm should be .284″. Unfortunately, when I ordered the LBT mold, I ordered it at .285″ not currently knowing the TJ’s barrel in 14″ twist would be too big. PHWEW! HOPE THIS MAKES SINCE. So now, I order a 10″ twist TJ’s barrel and upon receiving it, the barrels bore MIC’s at .2833″ which is pretty tight. Again, 7mm is .284. But in this case, tighter is better cause it’s easier to size down and not up. When the barrel was machined and installed, Doug Noble and I noticed that the gun dropped some major speed. Why you ask? The faster the twist, the more the friction on the bullet as its pushed forward. The slower the twist, the faster a projectile can move down the bore. This phenomenon really rears its ugly head with airguns. Remember, unlike a PB gun, we don’t work off of upwards of 40,000-60,000 psi. This gun works off of 3600 psi OPTIMALLY! And when the 1-10 twist is installed, the Corsair lost about 60 FPS. Doug made me one hell of a nice custom sizer at .2836″ but I was not happy with the performance of the 10″ twist barrel OVERALL. Not only was the speed down but the overall accuracy seemed to be only OK to me. Lastly for the 1-10″ twist, I bought a NOE mold in 7mm and it’s called the THOR bullet. This bullet has a very wide MEPLAT and once tested, AGAIN, I was less than happy with the barrel/bullet combos. So now, because I have too much free time on my hands, I decide to RE-INSTALL the 14″ twist barrel and to re-order a new LBT mold but this time, I would order it at size .287″ so I am only sizing down a thousandths and a half (so to speak…lol).
So this brings us to now. With the new LBT mold on its way and the 7mm TJ Liner with 1-14″ twist barrel installed, I cast up more THOR bullets and I head out for a quick shooting session. It became readily apparent that the 14″ twist was a better overall performer in 7mm ON THIS PLATFORM (corsair+). I actually shot a decent 1.5″ 100 yard group with those bullets and I couldn’t get anywhere near that with the 10″ twist. After going to South Carolina and hunting/shooting with RJ Porter, it was apparent that the 14″ twist barrel was the way to go. Not just because I killed a pig with it that weekend…lol! I was ringing steel plates out to 135 yards consistently with this barrel and the THOR bullets DESPITE THE FACT THAT I SAW “SPIRALING” OF THE THOR BULLETS ON VIDEO. I could not wait till the newer LBT came in due to its lower weight and shorter length which should improve the spiraling therefore accuracy (more on that later). So now, this past Monday, I head out and do some quick testing before the winds became unbearable. Initial testing and grouping have really shown promising and I am expecting groups to be really tight at extreme ranges. Or shall I say, my future goal for this gun is to remain under MOA at extreme ranges and so far, things look like with a little more attention to detail and some UPGRADES, I can achieve just that.
This group is with the 1-10 twist from a while back. The higher pressure was just so the projectile could maintain enough speed to stay accurate. And that is because of the much tighter 1-10 twist and these long bullets.
Here is the group from MONDAY at 55 yrds. Now, on this groups, you should note the different FILL PRESSURES and I will add this, there are slightly different hold techniques for the set of groups. YES, the Corsair is hold sensitive. Don’t ask why………I don’t know. But the small tiny groups was done with a light hold. As though I literally was holding a newborn baby. this gun has always been like this. Even brand new and in 308.
I must stress also that not only is there an upcoming change to the Corsair in the very near future but, these groups were also shot with UNSORTED BULLETS. The reason why I mention this is because, after coming home from this shooting excursion, I actually weighed many of my bullets and I found some in this batch that varied OVER 1+ grs. So I threw many of them back into the pot except for some. The ones is kept only varied no more than .5 a grain. So I immediately started recasting and this time, I kept all bullets that weight anywhere from 130.5 grs UP TO 131 grs even. So no more than half a grain. So when i shot the above groups, slugs could have weight 1 to even 2 grs different. NOT ANYMORE! I will be keeping a tight lid on my weight variances for each gun now. With long range, THIS IS NECESSARY!
STAY TUNED!December 12, 2014 at 12:08 am #215124
I am glad to see the rifle coming together. Consider also the Bob Sterne boat tails. I am making some progress on parts for the .308 Marauder. The firing valve is coming together nicely, and I am quickly developing an appreciation for good free machining steel…LOL
The issues and solutions I read y’all posting should make shaking it down a much faster process…and I am really looking forward to it.
DouglasDecember 12, 2014 at 12:36 am #215126
I’m patiently waiting on BOB’s 95 gr 7mm Boat Tail and BOY IS IT HARD. I just want to tell him to RELEASE THE DRAWINGS to Veral so at least I CANT BUY a mold. I’m ready, he’s not…..lol!
But as a backup, Doug already talked to veral about a lighter 7mm anyways so, if Bob doesn’t release that bullet, i just might have to move forward with my venture. I really want a lighter bullet in this gun.
Thanks for reading Doug and stay tuned for more to come soon!
CedricDecember 12, 2014 at 12:33 pm #215166quote Tofazfou:
Alright…in lieu of practicing patience, let me suggest finding the .257 drawings, and the .300 and .308 and work up some proportions and draw your own….:D Then run through the same calculator he uses and vary a few parameters( BT tail dia/caliber and meplat/caliber come to mind) and see where the BC goes.
I would try a 7mm myself, but with 500cc of air on board, and using the 95 or 110 gr he’s already penned for .308, I see no advantage to the smaller boolit; I will still have enough air on board for a reasonable shot string on a single charge. Sectional density sets the pressure requirements( for a given barrel length anyway ), and overall weight sets the air consumption, assuming the valve/porting is up to the task…and I think I have a proper one for the job underway…heh-heh-heh
In the meantime, consider a way to get a few folks to move closer to each other. I nominate SE Michigan for the locus, you, Doug, Bob, Sean, Lloyd top the list…December 12, 2014 at 5:00 pm #215171
MICHIGAN?! OK, only because its you, i will move that way……..lol! But, i can tell you, the wife WILL NOT BE HAPPY WITH THIS MOVE which probably means she would make me sell all my guns to FUND the move……… :butkick: :rofl:
I think the only thing BOB was saying about the 95 gr was that it was really WELL SUITED to the 14″ twist. My initial thinking on this is 1st, that i will loose BC numbers. That’s a big drop in length from 130 grs down to 95 ESPECIALLY in skinny calibers like 257-6.5-7mm calibers. And my goal is to shoot long range with this gun. Of course the 95 gr could reach way out there too but in my mind, there is some give and take between the 2 weights. When Doug and i just talked the other day, i asked him to talk to Veral about taking his LBT bullet in 7mm and making it shorter and he said he could. Doug and i both were thinking 115 grs because we are going to have it Hollow Pointed on one side of the cavity. Since i know that 135 gr pills can be stabilized in the 1-14 twist, going lighter by a little is just that much better suited to the twist. It also still gives the caliber some weight. The 7mm is going to be on the UPPER END of the 257 and the LOWER end of the 308 as far as WEIGHTS of projectiles and FPE goes. In 257, my TD makes over 180 FPE with 100 gr Spitzers. My Corsair in .308 make right at 250 FPE with 150 gr bullets. So the 7mm LBT bullets i have at 130 grs make around 230 FPE!
Oh yeah, i also know about the various drawing programs for bullets molds. I have a website that i’ve been using for a year or 2 that lets you draw and make your own bullets. As you change perameters, you can see how it affects the bullets. It’s MOUNTAIN BULLET MOLDSDecember 14, 2014 at 3:06 am #215250rj-porterParticipant
That 7mm is one badass gun. I’ve shot it and it hits what you want it to. I know it hits a pig with authority. BTW Ced hurry up with the video.December 14, 2014 at 8:04 pm #215291knifemakerParticipant
Howdy Cedric! Pak and RJ!!! Been playing with the .257 a bit, and the new barrel is smaller than what I have sizers for.
Cedric, your problems with the size of the 7mm reminds me that several people, including the fellow who makes the custom sizing dies said to try sizing to .0003 under bore dia? HuuuH??? Never thought of trying such a thing.
Any of you ever heard of this? 😕
KnifeDecember 15, 2014 at 12:48 am #215303
I can tell you this, for the 14″ twist barrel which, i have 2 lee sizer dies. One is about .0003″ over bore and the other is about .0005 or a little more UNDER bore. The Corsair does not like that one at all. It does OK and close ranges but the groups get far worse when you get out to 100-150 yards. Out of the 2 dies, the one slightly OVER bore obviously does better.
So someone out there who “CLAIMS” this will have to show more proof than taking their word for it. It goes against everything learned over the years.
Like i said, that size isn’t THAT much smaller than bore and may have some validity but, someone is gonna have to prove that one too us with more than words.December 15, 2014 at 12:58 am #215305knifemakerParticipant
That makes two of us buddy!
I would love to try an exact size. Say a .2573 bullet in a .257 bore! 😉
KnifeDecember 15, 2014 at 1:52 am #215307rj-porterParticipant
My 257 bullets are 2573December 15, 2014 at 9:56 pm #215362lambertusParticipant
As far as i know most of the guys who shoot bullets / solids with airguns on this side of the big pond use slightly bigger projectiles than the bore of their barrels.
I for one shoot .309 sized 150 grainers in my Corsair.December 19, 2014 at 12:48 pm #215601quote Tofazfou:
Given the relative cost of a handful of sizing dies compared to a rifle build I think I will run the experiment on the .308 to ~.0015 over groove diameter. Assuming a .308 groove, that leaves me .3077, .308, .3083, .3086, .3089 and .3092 for starters. Hopefully there will be a peak in the accuracy in the middle of that pack. Hopefully the velocity won’t be falling rapidly where the accuracy improves…LOL Hopefully….and so on and so forth. Then to decide if it is worth acquiring a mold I don’t have to size.
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