I have a Rem 788 that I need to re-barrel. This is a custom built rifle, it now has a 14 twist .243 barrel. It's chambered in 6mm Rem Imp and with 68 to 70 gr bullets it will shoot ragged one hole groups. This past year I started shooting F-class and to help buck the wind some what better I went to a Sierra 80 gr SBT. My load with the 80gr Sierra was 45grs IMR 4895 with a CCI BR-2 primer. This load is stout but no excessive pressure, vel is 3422.
I would like to buy another .243 barrel and chamber the gun in 6BR and shoot 105 gr Berger bullets, which will be much better suited for F-class than my current set-up. However, I have read about problems in the 788 specifically dealing with bolt compression which leads to case stretch and eventually excessive headspace. Also there has been problems with the bolt handles breaking off on the higher pressure .473 bolt face models.
What do you guys think? Will the 6BR work in a 788 or will I be wasting a new barrel, cost of gunsmithing and my time?
Thanks in advance
Jim
Jim,
I've built a lot of Palma/LR competitive guns. While the 788 Remington is probably not the first choice for a lot of guys, I don't think it's the worst option either. If the action and bolt have sufficient hardness and surface area for the chamber pressures, then I don't think you'd have much to worry about. I have to think Remington did enough homework to ensure the product is safe.
All too often shooters run a load to the extreme limits of pressure and then when stuff breaks, they can't face the fact that they made a mistake; they blame the equipment. Tough words but after almost ten years of doing this stuff, it's often the truth.
Your interest in the 6mm BR should produce good results. If you run with Norma brass ensure that who ever barrels the thing runs the bolt to breech face clearance a little on the conservative side. I always set these up with a clearance of .010". This has worked well in the past as Norma brass is (was anyways) always a tad thinner back in the web area and its good to support as much of the case as reasonably possible. I know of one domestically produced target rifle that failed to observe this fact and it resulted in a few guns shooting magazines out of the bottom of the receiver when the cartridge ruptured.
Experience is never cheap and stitches are trophies for the intense. . .
On feature about the little BR that will work in your favor and ease your concerns is that it is quite conservative on the case taper from the rim to the shoulder. This is a good thing, especially for high pressure cartridges as it allows the brass to bear against the chamber at almost a right angle. The best way I've found to take advantage of this surface contact is to avoid polishing the chamber to a mirror finish. 320 grit emery soaked in Kroil and mounted on a wooden or brass mandrel works great when spun at about 1000 rpm. It'll leave a finish that emulates a freshly honed cylinder block. This finish seems to "bite" well without "frosting" up the brass. Cases like the 22-250 have significantly more of a relief angle and this can result in more force being exerted on the bolt (and consequently, the locking lugs) which could peen the lugs over time I guess. Keeping the HS conservative will help mitigate this as well.
The way I headspace ALL my competitive guns is with the "Go Gauge/shim stock" method.
Chamber the barrel so that the bolt will close with a Go Gauge, but will just "stick" when a little piece of .001" thick shim stock is inserted into the bolt face. ( a little dab of grease greatly aids in keeping it in place as you insert it into the action)
This method does a couple things for you. One you know EXACTLY where your HS is (vs a Go/No Go gauge which has a mile of tolerance) so that if something changes, you know how much and after how many rounds. (assuming you keep a gun log book) Second, you can set your dies up using the same gauge and shim stock and have better control of just how much you resize your brass. You won't have a dimension per say (unless you can ding the go gauge on an optical comparator) but so long as you dedicate that gauge to that gun you have a standard to reference from. Well worth the $30 dollar investment in my book.
A 6mm 105 grain bullet is going to need a 1-8ROT barrel if it ever has any hope of stabilizing. I'm sure you knew that already. IF your using a VLD then a shallower throat angle is also advised. David Kiff from PTG makes excellent chamber reamers (and Go Gauges) just for these applications. I'd possibly consider a barrel with a "softer contour" on the lands/grooves that don't bite the bullet jacket quite as aggressively. The VLD type bullets commonly use a J-4 jacket material and it is quite thin. The high rotation rates generated by a 1-8 barrel and the potential for the bullet coming apart is elevated. Not trying to scare you, just be aware of it. I seem to remember being able to stoke mine up to about 2900fps with a 28" tube. This is in my 300meter free rifle built on a Nesika. I've heard of guys going as high as 3300 in other cartridges but I've never seen it myself. Right around 3K seems to be the norm.
Hope this helped and good luck.
