Need advice on testing during load development

[Jesse09]

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.

 

[bruce_ventura]

What gun are you shooting? Type of stock? Bedded?

What size group and muzzle velocity ES are you trying to reach (how good is good enough)?

 

[Jesse09]

What gun are you shooting? Type of stock? Bedded?

What size group and muzzle velocity ES are you trying to reach (how good is good enough)?

Thanks for the reply. My rifle is a custom, with a Broughton #4 contour and McMillan stock, professionally built and bedded by Jered Joplin of American Precision Arms.
Jered expects groups in the .25" range, but delivered it to me, unfired.

I would like the lowest MV (to prolong barrel life) that still takes full advantage of the flat trajectory this caliber can deliver (3400's). I'm not certain what you're asking in terms of ES, but of course a low Es indicates a more reliable point of impact.

As far as how good is good enough: I could have bought an off-the-shelf Tikka T3 and obtained sub-MOA with factory ammo (I've done four of them). I think the .5" range isn't asking too much with the current rifle.

Jesse

 

[Jesse09]

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.

 

[acloco]

IMHO, work your load up at 300 yards.

In my experience, I have walked right by great bullet/powder combinations by only working up loads at 100 yards. Had some leftover 100 yard load development rounds that I decided to shoot at 300. Low and behold, sub MOA accuracy.

The other reason....especially with the 270 WSM (actually, darn near every caliber, 243 and up), the difference between a 300 yard zero and 100 yard zero is not much.


Are you using 110 gr bullets? Only bullet that I found in 277, that is in the 3400 fps range.

Hornady Manufacturing Company :: Bullets :: Rifle :: Choose by Caliber :: .277 270 CAL :: 270-6.8mm .277 110 gr V-MAX® with Cannelure


If so, sight in a 200 yards. Bullet is 1" high at 100 and 5" low at 300.

Ballistics Calculator - Hornady Manufacturing, Inc

 

[Greyfox]

Having been a shooter of the 270WSM, I had a few thoughts about your post. Also, most of my load development and practice takes place in summer temperatures no too different than yours described down there in Atlanta. My first thought is that your are paying way too much in time and energy trying to conserve your barrel. The single best way to extend your barrel would be to choose a good high BC140-150 gr bullet driven to 3100-3200FPS. The trade off in flat trajectory, especially out to 300 yards with a hunting rifle would not be materially different. 3" high, 300 yard zero n my rifle had me in the the vitals of coyotes from 100 yards to 350 yards. I would also test the POI of your rifle hot, cold clean, dirty. You might be surprised and find out that POI doesn't shift. Mine doesn't. At the very least you will find out what the effect is, and then figure out what to do. Finally, getting good terminal ballistics on game with a 3500FPS light bullet on game between 100 and 500 yards can be tricky. I'm at 1000 rounds through my 270 WSM and groups are still .25-.5MOA. Just my experiences and opinion.

 

[Jesse09]

Thank you, acloco and Greyfox, for your thoughtful replies. I could have done a more thorough job of explaining both my situation and development plan.

This is my second 270 WSM, the first being a Tikka T3. Jered Joplin said he "couldn't believe" how badly shot-out that barrel was when he bore scoped it. It had a total of 586 rounds through it, and they were almost all with the Nosler 130 grain ballistic tip at 3100 fps. I had always allowed the barrel to cool between shots in recognition of the relatively short life I expected from this caliber. So, Greyfox, that's why I'm trying to do better this time around.

Acloco, I should have reported that "I think I've finished phase one of my load development". I now have enough seasoned brass to begin the next step: I'll first shoot from a clean, cold barrel at 100 yards, both to test whether or not this barrel requires foulers, and to set a tentative POI. My next groups will be at 300 yards. If all goes well, I'll work my way back through 250, 200 and 150 yards, trying to match the predictions of my ballistics software and to learn when the barrel needs cleaning. If the 300 yard testing is disappointing, it's back to the drawing board.

I am trying out the Barnes all-copper 110 gn TTSX after reading a lot of rave reviews that comment favorably on its being easy in establishing a load and showing great terminal performance at maximum muzzle velocity. (I also have a lifetime supply of IMR 4350.) I'm aware that it doesn't have a high B.C., but pretty much all of my shots will be taken between 200-325 yards on whitetail deer.

I've noticed, BTW, that the TTSX does not leave very much copper residue in the barrel. This is in line with the claim from Barnes, but may also be a tribute to Jered's barrel preparation.

It's all a learning experience, including the hard-to-believe .040" off the lands. Barnes tech support had advised me to start at .050" and work forward and back between .030" and .070".

 

[Jesse09]

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.

Jesse

 

[rcoody]

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, 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.

Jesse

I would say you are there.

 

[Jesse09]

Thank you, rcoody, for the comment. Yes, I'm there and it's been ridiculously easy. I have a total of only 90 shots on the barrel, including 20 commercial rounds that I fired just for a base of comparison to my hand loads.

I know the Broughton barrel blank contributed, but think most of the credit goes to the guys at American Precision Arms.

Jesse

 

[SidecarFlip]

Besdies, barrels are easy to swap out......