RRA Varmint A4

stovepipe · Posted: Mon Sep 13, 2010 11:11 am Post subject: Re: RRA Varmint A4

Dawgdad wrote:

OAL from case head to bullet tip is not a good way to measure... loads.(or any load for that matter)

It is- IF you plan on feeding from a mag. Otherwise I agree and that's a very cool pic D'dad. Cool

I hear MK's don't like big jumps and the ogive Is pretty far back on some so the jump is multiplied....

I aint got no chamber lentgh tools so I'll put a bullet in an primed neck sized case and close the action on it slowly then extract slowly and check fer touch and deduce OTL lentgh from there, then, check a few loaded rounds to be sure, esp after the bore heats up.

YMMV! Very Happy

44marty · Posted: Mon Sep 13, 2010 12:32 pm Post subject: Re: RRA Varmint A4

Dawgdad,
Nice illustration. I have read the "just off the lands" theory ad nauseum in books and online. What I can't figure out is why there are exceptions to the rule. All benchrest shooters I know load as you do.

How in heck do Weatherby's have such good accuracy with standard (magazine-length) cartridges??? I tested a series of 5 rounds each in .015" steps loaded single-shot into my .300 WBY mag that ran from .020" off the lands all the way back to mag-length and all shot beautifully tight groups. There was no discernable difference between the group sizes. I ran the same test a second time just to be sure and had the same results.

I also checked the jump in my .204 Ruger, and it is HUGE. Depending on bullet profile, it can be almost as much as the WBY. The rifle still puts all the rounds in one tiny hole. If I really take my time and do my part, it is often very hard to tell difference in the hole in the paper between a single round and a 5-shot group.

I am not complaining, but do you have any idea why ???

Dawgdad · Posted: Mon Sep 13, 2010 2:43 pm Post subject: Re: RRA Varmint A4

Yes I do Marty... but like all knowlwdge I borrowed it from someone else.

Eric Stecker of Berger Bullets penned this little treatise on bullet jump and the VLD (very low drag) bullets.

A lot also comes from how true the freebore is and how concentric you loaded the rounds.

Quote::

Getting the Best Precision and Accuracy from VLD bullets in Your Rifle

Background

VLD bullets are designed with a secant ogive. This ogive shape allows bullets to be more efficient in flight (retain more velocity = less drop and wind deflection). While this result is desirable for many rifle shooters the secant ogive on the VLD bullets produces another result in many rifles. It can be difficult to get the VLD to group well (poor accuracy).

For years we encouraged shooters to use a base of cartridge to end of bearing surface OAL (I will use the term COAL to represent this dimension) which allows the VLD to touch the rifling or to be jammed in the rifling. This provided excellent results for many shooters but there were others who did not achieve top performance with the VLD jammed in their rifling. These shooters were left with the belief that the VLD bullets just won’t shoot in their rifle.

Other groups of shooters were discouraged by our recommendation to touch the rifling. Some of these shooters knew that at some point during a target competition they will be asked to remove a live round. With the bullet jammed in the rifling there was a good chance the bullet will stick in the barrel which could result in an action full of powder. This is hard on a shooter during a match.

Yet another group of shooters who were discouraged by our recommendation to touch the rifling are those who feed through magazines or have long throats. Magazine length rounds loaded with VLDs could not touch the lands in most rifles (this is the specific reason that for years we said VLD bullets do not work well in a magazine). When a rifle could be single fed but was chambered with a long throat a loaded round that was as long as possible still would not touch the rifling.

Until recently, shooters who suffered from these realities were believed to be unable to achieve success with VLD bullets. Admittedly, we would receive the occasional report that a rifle shot very well when jumping the VLD bullets but we discounted these reports as anomalies. It was not until the VLD became very popular as a game hunting bullet that we were then able to learn the truth about getting the VLD bullets to shoot well in a large majority of rifles.

After we proved that the Berger VLD bullets are consistently and exceptionally capable of putting game down quickly we started promoting the VLD to hunters. We were nervous at first as we believe the VLD needed to be in the rifling to shoot well and we also knew that most hunters use a magazine and SAMMI chambers. Our ears were wide open as the feedback was received. It was surprising to hear that most shooters described precision results by saying “this is the best my rifle has ever shot.”

We scratched our heads about this for awhile until we started getting feedback from hunters who were competition shooters as well. Many were the same guys who were telling us for years that the VLDs shoot great when jumped. Since a much larger number of shooters were using the VLD bullets with a jump we started comparing all the feedback and have discovered the common characteristics in successful reports which gave us the information needed to get VLD working in your rifle. We were able to relay these characteristics to several shooters who were struggling with VLD bullets. Each shooter reported success after applying our recommendation.

Getting the Best Precision and Accuracy from VLD bullets in Your Rifle

Solution

The following has been verified by numerous shooters in many rifles using bullets of different calibers and weights. It is consistent for all VLD bullets. What has been discovered is that VLD bullets shoot best when loaded to a COAL that puts the bullet in a “sweet spot”. This sweet spot is a band .030 to .040 wide and is located anywhere between jamming the bullets into the lands and .150 jump off the lands.

Note: When discussing jam and jump I am referring to the distance from the area of the bearing surface that engages the rifling and the rifling itself. There are many products that allow you to measure these critical dimensions. Some are better than others. I won’t be going into the methods of measuring jam and jump. If you are not familiar with this aspect of reloading it is critically important that you understand this concept before you attempt this test.

Many reloaders feel (and I tend to agree) that meaningful COAL adjustments are .002 to .005. Every once in a while I might adjust the COAL by .010 but this seems like I am moving the bullet the length of a football field. The only way a shooter will be able to benefit from this situation is to let go of this opinion that more than .010 change is too much (me included).

Trying to find the COAL that puts you in the sweet spot by moving .002 to .010 will take so long the barrel may be worn out by the time you sort it out if you don’t give up first. Since the sweet spot is .030 to .040 wide we recommend that you conduct the following test to find your rifles VLD sweet spot.

Load 24 rounds at the following COAL if you are a target competition shooter who does not worry about jamming a bullet:
1. .010 into (touching) the lands (jam) 6 rounds
2. .040 off the lands (jump) 6 rounds
3. .080 off the lands (jump) 6 rounds
4. .120 off the lands (jump) 6 rounds

Load 24 rounds at the following COAL if you are a hunter (pulling a bullet out of the case with your rifling while in the field can be a hunt ending event which must be avoided) or a competition shooter who worries about pulling a bullet during a match:
1. .010 off the lands (jump) 6 rounds
2. .050 off the lands (jump) 6 rounds
3. .090 off the lands (jump) 6 rounds
4. .130 off the lands (jump) 6 rounds

Shoot 2 (separate) 3 shot groups in fair conditions to see how they group. The remarkable reality of this test is that one of these 4 COALs will outperform the other three by a considerable margin. Once you know which one of these 4 COAL shoots best then you can tweak the COAL +/- .002 or .005. Taking the time to set this test up will pay off when you find that your rifle is capable of shooting the VLD bullets very well (even at 100 yards).

Regards,
Eric Stecker
Master Bulletsmith

Dawgdad · Posted: Mon Sep 13, 2010 2:53 pm Post subject: Re: RRA Varmint A4

stovepipe wrote:

Dawgdad wrote:

OAL from case head to bullet tip is not a good way to measure... loads.(or any load for that matter)

It is- IF you plan on feeding from a mag. Otherwise I agree and that's a very cool pic D'dad. Cool

I hear MK's don't like big jumps and the ogive Is pretty far back on some so the jump is multiplied....

I aint got no chamber lentgh tools so I'll put a bullet in an primed neck sized case and close the action on it slowly then extract slowly and check fer touch and deduce OTL lentgh from there, then, check a few loaded rounds to be sure, esp after the bore heats up.

YMMV! Very Happy

Just do not use the shortest bullet in the box to set up the OAL doing it that way....

slimjim · Posted: Mon Sep 13, 2010 4:09 pm Post subject: Re: RRA Varmint A4

Dawgdad, thanks for all the good information. It was a good read.

I was more interested in your COAL to see if there were any magazines I could find that might provide a load length long enough. My Magpul thermal-plastic mags are great but 2.240" is pretty much the limit. I've heard that the PRI mags might let you load to 2.3+ a little.

Dawgdad · Posted: Mon Sep 13, 2010 6:09 pm Post subject: Re: RRA Varmint A4

I will tell you that my loads are over 2.4++" with these bullets. No magazine will hold them and they were not designed to be loaded down to mag length. The shape of the point of the bullet is such that the ogive would be below the case mouth and it would be impossible to get a grip on the bullet if the tip was set to mag length. Plus even if you did manage to get the bullet to seat you would have taken up so much case space in the .223 case you would not get enough powder to get enough velocity to make a good 600 yard load.

44marty · Posted: Mon Sep 13, 2010 7:08 pm Post subject: Re: RRA Varmint A4

Thanks, Dawgdad, a very good read.

slimjim · Posted: Mon Sep 13, 2010 8:06 pm Post subject: Re: RRA Varmint A4

Dawgdad wrote:

my loads are over 2.4++" with these bullets. No magazine will hold them

The wheels are turning. I could design a magazine that allowed this to load. It would be unique but could be done. Usually, when I think of something new, someone has already done it. A google search didn't come up with anything but that doesn't mean that it hasn't been done already.

Dawgdad · Posted: Mon Sep 13, 2010 8:48 pm Post subject: Re: RRA Varmint A4

One more point to consider.. I had some shots going off call at 600 last weekend so I just measured my chamber again tonight. After 1396 rounds the chamber had receded .025". Now I have to re set the bullet seater to account for the extra distance to keep the jump at .015". I should have checked it sooner and been growing to 'chase the lands' instead of waiting for the loss of points in a match. BTW - it is still a hammer at 200 and 300 yards with mag length bullets.

Suzanne · Posted: Mon Sep 13, 2010 9:08 pm Post subject: Re: RRA Varmint A4

DawgDad!! I think that clears up a problem with the Swiss Schmidt Rubin k-31. I think it had a secant ogive bullet design. I've never seen any GP-11 ammo that it was designed to use but when I started reloading for it, using the published data on OAL, I found there was no way the round would chamber, it was always way too long. The tangent ogive bullets I am using won't chamber (bolt won't close) because the shape isn't right. When I seat a bullet into the brass I have to seat it well past the crimp on the bullet. Thanks to the article you submitted and another I found HERE I have a better understanding of why I need to find a secant ogive bullet to properly fit the chamber. It's funny no one seems to mention this in the Swiss forum I'm on, but they do mention that the GP-11 ammo is the most accurate to use in the rifle. Well DuH!! because, it fits the chamber! I'm gonna havta razz some people over there.....

Thanks Dawg

Suz

Dawgdad · Posted: Mon Sep 13, 2010 9:56 pm Post subject: Re: RRA Varmint A4

You are welcome Suz.

I did not want to go there all at once since some of this is hard to get your head around unles you are loking at a cut away chamber and barrel and trying differnt things. The Secant VLD bullets like the Berger, Hornady A-max and 80 SMK's will have very long COAL's compared to the Tangent design bullets but the actual Ogive jump is not as different.
OK slim here are some real numbers...
My long range bullets are A-max 75's have a COAL of 2.435" and a ogive length of 1.905"

The magazine lenght "short range" loads with 77SMK's I use at 200 and 300 are 2.240"COAL
with the Ogive length of 1.840"

The COAL difference is 0.195" while the actual bullet jump difference is only .065" since the bullet profile is different for each type of bullet

To get back to Marty's issue the tangent designed bullets are much less picky about the jump since they have a longer bearing surface and will "straighten them selves out " in the throat and barrel while the secant profile bullets can get squirrely and will be pitching and yawing if they are not very concentric with the bore. (runnout under .003") When they come out right they have a huge advantage at longer range.

But they take a little work to get er done. If you do not want to take the time to craft a long range (500+ yards) the "short line" loads do work out to 600 but the wind drift error for missing a wind call by a couple of mph is the difference between a hit and a miss.

slimjim · Posted: Tue Sep 14, 2010 3:35 am Post subject: Re: RRA Varmint A4

Dawgdad, thanks for all this good "understanding" Hopefully, this RRA Varmint upper will give me some good experience and be a good shooter. I think I'll pick-up a pack of Hornady 75gr A-Max tomorrow when I drive by Cabela's. After a good barrel break-in, I'll start to work some single shoot loads. For now, I've got the 69gr SMK Fiocchi Match for the 300 yard work and to play with the wind at 500 yards. The 77gr SMK does have a better BC but the 69gr also work in my 1:9 twist - the 77gr not so well.

Dawgdad · Posted: Tue Sep 14, 2010 6:48 am Post subject: Re: RRA Varmint A4

75 A-max - 24.5 gr RE-15 or 24.2 of Varget = hammer

Dawgdad · Posted: Tue Sep 14, 2010 8:26 am Post subject: Re: RRA Varmint A4

Suz IIRC K31's have like zero freebore so any bullet you use will be into the lands. I would look at the Speer 125 TNT HP for a reduce weight lighter kicking bullet than the 174 pill in the GP11.

BTW the GP11 is definitel on the secant profile pointy side

stovepipe · Posted: Tue Sep 14, 2010 8:43 am Post subject: Re: RRA Varmint A4

Dawgdad wrote:

This is also why sometimes people think their seater die is messed up because it cannot hold an OAL under .010". Quality seater stems do not seat on the tip but have an opening that is close to the ogive.

Great point. Pulled my LEE seater apart for my 300 and yep- stem has a nice deep hole. Seats bullets using the ogive, just above it actually. Cool