NEED ADVICE ON TESTING DURING LOAD DEVELOPMENT

[Harley]

I’m developing a hunting load for a new 270WSM. Muzzle velocity is from low 3400’s to low 3600’s, with a projected barrel life anywhere from 500-1000 rounds. Because it’s a barrel burner, I don’t want to spend any more shots, generating any more heat, than I have to while developing the load.

Here in Georgia the ambient temperature (I’m on the bench at daybreak) will rise from the low 70’s F to the upper 80’s F during the time I’m shooting.
My usual procedure is to load five 3-shot groups, varying only one component (seating depth or powder charge) among the groups. I’ll cool the barrel between shots (not groups) by placing the rifle in a modified cooler. I shoot “round robin” groups, meaning I shoot only one shot at each target before moving to the next, finally completing all five groups in about three hours.

So, the barrel is cooled to pretty much the same temperature for each shot; however, the ambient temperature is steadily climbing, so that there may be as much as a 12*F rise between a group’s first and third shot.

I could eliminate the effects of the rising ambient temperature by firing all three shots at a given single group in the space of a few minutes, then cooling the rifle before moving on to the next group. That would mean, though, that the barrel temperature would rise a lot higher than I’m comfortable with, given the 270WSM’s high MV. I’m concerned that: (1.) I’d be shortening barrel life at those temperatures, and (2.) the rapid heat build-up between shots 1 and 3 would distort the point of impact on the target.

Remember, I’m developing for hunting, not benchrest; so, I want a load that consistently delivers its best one shot at a time from a cold (or ambient temperature) barrel.

Thanks for your recommendations.

[Harley]

I didn't hear from anyone, but decided to test a different procedure this morning:

I shot one 3-shot group at a time, cooling the barrel in my rifle cooler for five minutes between shots. This eliminated the extended rise in temperature that results from round robin shooting.

This was my second time out with the new rifle, and I've finished load development. I settled on a muzzle velocity of 3490 fps, which is fast enough to require an adjustment of only one MOA, plus or minus, out to more than 300 yards.

After cleaning and fouling, I shot three test groups of three shots each:

.176"
.850"
.323"

I think I can be more consistent after the barrel is broken in and after all the new brass is fire-formed.

If anyone wants a referral to an excellent custom rifle maker who delivers on time, let me know.

[7mmfreak]

1 MOA of elevation to 300yds or more? I'm guessing you are shooting a 110gn (ish) bullet. My .257 Wby Mag wouldn't do that at similar velocity. The only thing I have shot that will do that is a .22-250 Improved, .220 Swift, or .243 Win at 4000fps. I gave up on that notion and shoot heavier bullets around 2800-2900fps.

As far as load development I follow the Audette method but instead of 1 round per charge I like 2-3. I think it is the easiest way to get a rock solid load without doing a lot of shooting.

Who's the smith?

[Harley]

Good guess; I'm shooting the 110 grain Barnes TTSX.

The gun maker is Jered Joplin, president of American Precision Arms in Jefferson, GA. www.americanprecisionarms.com

I supplied a new action and a new stock; Jered ordered a Broughton #4 contour blank. He told me I would have the completed rifle, including bedding and Cerakoting, in 90 days. He missed that estimate by three weeks because the new reamer was delayed by its supplier. Anyone who has waited years (as I have) for a custom rifle knows how rare it is to have the work done in a timely manner.

It was delivered to me unfired, but Jered promised it would shoot .25"; I don't doubt it.

[7mmfreak]

APA has a good reputation and I'm sure you are pleased. 90 days is a good turn around and 3 weeks over on a reamer is understandable. I'm a month over delivery time on a Manners stock right now. Manson reamers will often hook you up if you are in a jam.

[Harley]

I sympathize on the Manners stock; I just got lucky with my own McMillan: The first time I visited their web site they just happened to have two on hand. I ordered one of them, immediately, then returned to the description page. In that length of time the other one had been sold, also.

BTW, you might be interested in the details of the scope I bought for it. It's the new Vortex Razor HD Gen II 3-18X50. It's FFP, with MOA reticle. I love everything about it except the 46 ounces. That brings my new rifle up to 11.5 pounds, not exactly what you'd carry sheep hunting. The quality and features are enough to make a Nightforce owner cry.

[Harley]

Even though this thread has generated almost no interest, I thought I'd finish it with a report on this morning's shooting.

The temperature was a steady 75*F; the humidity was 100% with a slight drizzle (causing my glasses to maintain a constant fog), and I was shooting from a portable bench that mirrored each heartbeat on my reticle. The good news was that there was no measurable wind.

I first shot at 100 yards to set point of impact and to observe how many shots from a cleaned barrel were required before the groups settled. I found that the first three shots were sub-moa (.600"), indicating that this barrel needs no foulers before hunting.

After making a single vertical adjustment (compensating for the absence of the MagnetoSpeed chrony I had used during load development) I fired three shots at 300 yards, cooling the rifle in my cooler for five minutes between shots. That three-shot 300 yard group measured .946".

I then worked back through 250, 200 and 150 yards, confirming a maximum plus or minus 1 MOA over the entire range to 300 yards.

Harley

[7mmfreak]

Is your 1 MoA a group size or elevation adjustment? You are sub MoA in precision but I still don't see 1 MoA of elevation getting you to 300yds.

[Harley]

I apologize for not posting sooner, but didn't receive a notification.

Here's all I can tell you:

Barnes TTSX 110 gn
Muzzle velocity: 3490 fps
Height of sight above bore: 1.869"
Zero at 250 yards
MOA is ~ + 1.52 at 100 yards (This is an elevation measurement above point of aim.)
MOA is ~ - 0.87 at 300 yards (This is an elevation measurement below point of aim.)

I have verified the above from the bench.

Harley

[7mmfreak]

I guess we just think about it differently because that is most certainly 2.39 MOA from 100 to 300 yards, not 1MOA plus or minus. You have a 250yds zero with 1MoA plus a half and minus nearly a whole at 300. Like I said, the only rounds that get to 300 yards with about 1MOA of elevation are going 4000fps or faster.

[Harley]

You're right, we think differently. On August 14, I said "...require an adjustment of only 1 MOA, plus or minus...". I never meant to define a parabolic arc of one inch from the muzzle to 300 yards. The adjustment I referred to was from a "dead hold" at any given distance between the muzzle and 300 yards.

Glad we can put this to rest.

[7mmfreak]

You can't quote "dead hold" when you didn't say, "dead hold". You said,"I settled on a muzzle velocity of 3490 fps, which is fast enough to require an adjustment of only one MOA, plus or minus, out to 300 yards or more" without making mention of vertical offset. I made the assumption of 100yds, POA/POI, since it is standard and you didn't differentiate. Regardless, you have a nice rifle but it isn't a laser gun and add another 200 yards and you'll figure it out.

[Deleted]

I didn't spell story

[7mmfreak]

Lol

[Harley]

1.When I said "dead hold", I wasn't intending to quote any earlier reference, just framing an expression in an attempt to clarify my thinking for you.
2.I never claimed I had a "laser" rifle. My reason for starting the thread was just to ask for comments on barrel heating and cooling.
3."Add another 200 yards and you'll figure it out." I have no idea what you think I can figure out, but it does sound mean-spirited. In all the years I have been a member of this forum, I can think of only a few exchanges that were intentionally adversarial. I have absolutely no interest in continuing down this path.

[7mmfreak]

I'm not trying to be adversarial and I'm sorry if you are upset. I don't think anyone who knows me would call me mean spirited. Your gun is no doubt a screamer and it may suit your needs without fail although I am not a fan of light bullets at lightning velocity because your decay will be faster than with a heavier, more aerodynamic bullet (what I meant by add another 200yds). I was just saying it isn't as flat as you made it sound but I now understand what you meant. Again, sorry if I hurt your feelings.