Rosecrans1 Wrote:Mel, you may or may not get the significant increases in MV with a 28" barrel on your bolt rifle. The increase in the barrel length still acts as additional chamber area before the bullet exits the muzzle. Your gas pressures are diminishing after that initial spike. I would guess you hit a point of diminished returns though it may or may not be at that barrel length. It may also increase your chamber pressures too. Just be careful out there!

Just thinking............with a Magnetospeed at the end of a 28" barrel, from a distance, people will think you're a civil war reenactor!

mel Wrote:going to email pf one more time my internet at home has been exceptionally bad the last few days so wondering if the email didnt send right

A5BLASTER Wrote:I would call them instead. From what I'm understanding they are working with a short staff issue still.

But if you call most times Mark answers the phone on the second ring.

mel Wrote:ordering my lower ,billet upper and hand guard tonight though i may reconsider building a dedicated lower for it , ive already got a dpms panther lower and my skelotinized lower i can put the upper on, i can always buoild a dedicated lower for it down the road

mel Wrote:so while i still have time to change my mind im wondring if i should change my twist rate , i picked 1-8T but wondering if i should choose something else since this thing is going to be shooting 130/140 and possibly slightly heavier pills

tdbru Wrote:Mel,
go to either hornady's ballistic calculator 4DOF or the berger twist rate calculator. put in the bullet, MV and twist rate and see what the gyro stability number looks like. in Lyman's book on long range shooting they have an article by, hope i get the name right, Dave Emary who use to be the chief ballistician at Hornday. in that he says get a twist rate that you get gyro of 2 for what you're using. i'd been shooting Sierra 142s in a 260 Rem with 1-8 and the gyro was less than 2. and my groups weren't super either. tried the hornady 130 eldm's and the gyro went to either 2 or like 1.98 for my mv and the groups got tighter. maybe something to what Mr. Emary is saying. anyway, due to what i read, right or wrong, and very limited experiences i'll limit my 1-8 twist to the 130gr. VLD bullet length or shorter. it's actually bullet length, not weight, that drives the twist rate. for my 142s i should have been using 1-7.5 or 1.7. don't recall off the top of my head. your mileage may vary of course, since each barrel is a law unto itself as far as how it groups due to many variables. but the gyro number is a calculation. if i recall both Hornady and Berger say if you get above 1.5 you're good. but they're both trying to sell bullets. if Hornady's former chief ballistician thinks 2.0 is where to run, i'd tend to use that recommendation, or weight it heavily. the long range guys, like F-class or PRC are running very long 6.5 VLD bullets with screw thread twist rates. very long, like in the 150gr. range VLDs in 6.5mm. so it depends on what bullet length you want to run as to what twist rate to run. however, that said, the very long 6.5 bullets will come out of the Grendel quite slowly, so you'll need LOTS of scope MOA range or a 40-60 moa rail or both to shoot then long long range like you do. and you may have quite a powder compression issue if you load to fit in your AR mag or you may have to cut back on the powder amount quite a bit since a super long VLD seated to mag length will stretch back into the case quite a ways. so that will be a compromise as well. most cartridges have an "optimum" bullet weight for the bore diameter and case capacity. with the 6.5 Grendel i feel that that optimum range is in the 110gr. - 130gr. range, which will work well with the 1-8 twist you picked i think. my opinions of course and feel free to disagree, won't bother me at all. just bringing some things up to discuss or think about.
-tdbru