'Jump' to Rifling Distance for Magnum Hunting Rifle Loads?

[Mountain]

I've been working up some 'target' loads for Dad's old 7mm Rem Mag model 70 Winchester- early post '64 version. I've seen quite a few recommendations for ~3.29" - 3.3" C.O.L., but for 175 gr SMK's this seems a bit short for my chamber. Via a Hornady overall length gauge, the SMK's engage the rifling at ~3.52" C.O.L. For accuracy, I typically see recommendations for a 'jump' of a few thou- maybe ~.005" to .012" at most; but this may be for target barrels / chambers.

At a 3.29" C.O.L., I can squeeze a .89" 5-shot 100 yd group out of the ol' gal under less than ideal conditions (some wind, only a 7X scope & tired eyes). That's not bad but I'd like to do better. Seems like a jump of .230" is pretty excessive and I'm killing some potential accuracy with this. I absolutely will not jam the projectile into the rifling to avoid a nasty over-pressure condition; but for reference, only ~.200" of the 175 SMK is seated in the neck at 3.52" C.O.L.

Anyone have any rules of thumb or at least advice regarding jump distance for magnum rifles with plain jane hunting profile barrels / chambers? Reason I'm doing this is to develop loads for a light hunter-class benchrest match. If anyone really does their homework for a SAKO, Kimber, Sendero, etc. light barrel rifle, they should be getting ~.5" groups at 100 yards. I'd like to be close to that. Yes, I swapped scopes and will use a VX-2 16 power scope instead of the old VX 7 power. As always, thanks!

 

[Stape]

I've always started at the recommended COAL and then seated farther and farther out in increments until I found that "sweet" spot. I measure the COAL before it makes contact into the lands by taking 3 partially resized cases and seating a bullet into them obviously longer than the chamber. I mark them with a sharpie around the neck and proceed to chamber each round, pushing the bullet into the case as the bolt closes.

i extract the rounds and measure them. Ideally, all three measure the same after this effort, and often they do.

Now.......that is the measurement for that rifle with that bullet. This is important, use a bullet comparator, this will measure your loaded round from the base of the case head to the rounds OGIVE, this is the part of the bullet that the shank transitions to the tip, where it starts to curve out and become "7mm" or whatever the caliber is. For example, I can load almost any bullet under 60gr over any powder that will give me 2,700fps, as long as I seat said combo to 1.90 base to ogive, I will get MOA out of my .223 varmint rifle.

Key is knowing what your rifle likes, and seating depth and bullet has more to do with it than anything in my experience. COAL can change between different styles/weights of bullets, but the measurement from base to ogive never changes and remains consistent.

Sorry if I covered things that were glaringly obvious to you, I don't know you or your experience so not trying to insult you or anything.

 

[Mountain]

No problem, Stape; and thanks for the post. Yes, I'm already doing this for other rifles / calibers. The Hornady gauge and caliber-specific cutaway cases short cuts most of the steps you outline above, but when folks run across this topic in the future your process will be very helpful to someone without the gauge. Via the gauge, I will know exactly when the bullet engages the rifling. Essentially the barrel takes the place of the ogive comparator.



In my case for the old Win 70, that point seems way the hell out there. At a commonly recommended COL, I still have .23" to go before the bullet engages the rifling. I'll assume it's a factor of having a very aerodynamic bullet shape in a rather generous chamber designed to accommodate relatively heavy and 'fat' hunting loads. One more issue that concerns me: Even with a fairly long 175 SMK, there's not a lot of bullet seated in the neck.

I'm probably going to go with ~ .050" to .075" back from jamming / engagement. Even with some variance in ogive, for a match bullet like the SMK such a 'jump' will be well clear of jamming no matter what. Sub MOA is really not that bad considering this is a hunting rifle, but I'm trying to see if I can work a little more magic and hit close to .5 MOA. I think by any measure, closing in from .230" out can only help. I don't have enough gunpowder and projectiles to do this a couple thou at a time as a lot of folks recommend, LOL. Unless I get some compelling advice not to, I plan to try first .075" out, then .050" out.

 

[jasons]

No idea on the magnum stuff but SMKs in .223 seem to like about .010 to .020. They seem to like to be pretty close but not jammed.

 

[Stape]

Mountain, I've always gone by a general rule of always seating your bullet into the case at least the diameter of the bullet. Meaning if you have a .308 bullet, it should be seated at least .308 into the neck. I've loaded rounds long before, where there was just enough bullet in the case for the neck to hold it, and couldn't figure out why my groups dropped off. Then I read that tidbit above and used the advice, choosing another bullet weight/profile, to where I could seat enough into the neck AND reach my OAL goals, and my groups shrunk right back down.

 

[mac1911]

Mountain, I've always gone by a general rule of always seating your bullet into the case at least the diameter of the bullet. Meaning if you have a .308 bullet, it should be seated at least .308 into the neck. I've loaded rounds long before, where there was just enough bullet in the case for the neck to hold it, and couldn't figure out why my groups dropped off. Then I read that tidbit above and used the advice, choosing another bullet weight/profile, to where I could seat enough into the neck AND reach my OAL goals, and my groups shrunk right back down.

My dad's same advice to me..... also your limited to what max AOL will work in the magazine.
I can hear my Dad now.... "ahh what you do'n there trying to shoot that hunt'n gun like a fancy target shooter" My Dad was the classic " right tool for the job" school of thought.
I run my 30-06 loads in my 1903a3 just shy of magazine capacity so,they function.
I forget how long at the moment. I was using Hornady 168gn Match.

My dad was also big on "point blank range" and zeroing at a distance that covered your range.
My dad's hunting rifle was zeroed with the cross hairs on center mass that set basically got you a hit in the kill zone 50-230ish yards ( the most you would be shooting at in our spots might be 250) .
Single load that's another story.

Are you doing rapid fire bench match. I see some of these bench shooters with the right eject left load port and basically bang out the rounds as fast as possible.

I don't have a real accurate bolt gun. My 1903a4 clone with new,barrel I is my most accurate bolt gun. I found no measurable gain loading long with that rifle. Although I'm not sure that rifle/scope/skills will do,much better than 1 moa anyway.

 

[Mountain]

Good reminder to seat at least the diameter into the neck. My .075" jump should do that- more or less right on the money. The .050" will be a little off. We'll see how they do today. Planning on a trip to the range late this afternoon. If either beats ~.9 MOA that will be an improvement.

 

[Mountain]

Success! And... The NES brain trust is once again correct.

I was beginning to get a little worried about swapping scopes earlier this week. I don't have a boresighter and my first shots hit the berm but nowhere near the target. I burned up some heavy (ouch!) oddball hunting rounds and even a couple of my BR rounds to get well on paper at 50 yards.

Left my spotting scope in the truck and just used the 16X Leupold to check my progress at 100 yards. First group looked great- these were the .075" jump loads. Better seated into the cartridge neck but still a big jump. Went to the .050" jump loads and immediately I could see that some negative harmonic was in play, spreading out my group.

Took a caliper to my groups back home. .050" jump produced a .984" group. Really not that bad but no better than the .230" jump. Either a concentricity issue with too little bullet in the neck or just a bad combo. The .075" jump load group measured .451" at 100 yds. Earlier while messing around to zero the scope at 50 yds, I shot a couple of these rounds without scope adjustment and they were right on top of each other. Call me crazy but this load 'felt' better- the recoil was a little less and seemed straight back and up vs. other loads that seemed a little wild. Keep in mind this is a lightweight rifle, especially for 7mm RM.

So a little bigger jump but more bullet seated into the neck did the trick to bang in a group less than .5 MOA, which exceeds the intended purpose of the rifle. Yes, overkill for hunting but it's fun (and cheap) to tweak an old hunting rifle and its loads to get good results on paper. Even better, I have a few leftover longer loads that I can simply re-seat to the .075" jump.

 

[mac1911]

Success! And... The NES brain trust is once again correct.

I was beginning to get a little worried about swapping scopes earlier this week. I don't have a boresighter and my first shots hit the berm but nowhere near the target. I burned up some heavy (ouch!) oddball hunting rounds and even a couple of my BR rounds to get well on paper at 50 yards.

Left my spotting scope in the truck and just used the 16X Leupold to check my progress at 100 yards. First group looked great- these were the .075" jump loads. Better seated into the cartridge neck but still a big jump. Went to the .050" jump loads and immediately I could see that some negative harmonic was in play, spreading out my group.

Took a caliper to my groups back home. .050" jump produced a .984" group. Really not that bad but no better than the .230" jump. Either a concentricity issue with too little bullet in the neck or just a bad combo. The .075" jump load group measured .451" at 100 yds. Earlier while messing around to zero the scope at 50 yds, I shot a couple of these rounds without scope adjustment and they were right on top of each other. Call me crazy but this load 'felt' better- the recoil was a little less and seemed straight back and up vs. other loads that seemed a little wild. Keep in mind this is a lightweight rifle, especially for 7mm RM.

So a little bigger jump but more bullet seated into the neck did the trick to bang in a group less than .5 MOA, which exceeds the intended purpose of the rifle. Yes, overkill for hunting but it's fun (and cheap) to tweak an old hunting rifle and its loads to get good results on paper. Even better, I have a few leftover longer loads that I can simply re-seat to the .075" jump.

Nice to see it work out for you.
If your ever in doubt about your scope set up a target at 25 yards.
Most larger cal rifles will be close on paper @ 100 if you zero between 1/2" to just under 1" low at 25 yards.
My dad was pretty darn good at zeroing scopes. He would have liked what modern scopes have to offer these days.
He would zero in 3 shots or less @ 25 then fine tune at 100
Unless he was setting up a scoped hunting rifle. Then he had his own zeros.

 

[Mountain]

Yeah, I should have set up a big target at 25 yards. Next time...

 

[mac1911]

Yeah, I should have set up a big target at 25 yards. Next time...

I use the painters paper rolls put a fresh clean backer on the target frame. http://www.homedepot.com/p/Trimaco-35-in-x-140-ft-Brown-Builder-s-Paper-35140/202040749 I will often just draw the target right on the paper. Been looking for a roll of 1" graph paper to do some load testing want a wide roll like above.
Im to lazy to draw out the graphs and my printer sucks and cost me a small fortune in ink to print targets.

Like this https://m.youtube.com/watch?v=TiOpQY2ORo4
I like the reticle on this scope.

 

[Mountain]

Good idea for the paper rolls. I'd just use one of the stick-on bullseyes over that. Yeah, roll of 1" graph paper would be nice. I don't know the size of the grid, but I think you could find some cheap (garage sale?) wallpaper with a grid on the back- might be 1".

Sighting in 2 shots? Where's the fun in that? LOL. Not so easy to do when swapping scopes & the shots are going way off paper. I do like the method.

BTW, won the light class BR match today with the 7mm RM that prompted my original post. Had a little vertical stringing (downward as the barrel got hot). Comped for that a little, shot to shot. I was one of the RSO's and didn't shoot heavy. Helped a father & son to shoot my heavy AR since they had some trouble with the rifle they brought- I think one of them scored 2nd in heavy. Windham VEX AR is a tack drivin' son of a gun...

 

[mac1911]

Good idea for the paper rolls. I'd just use one of the stick-on bullseyes over that. Yeah, roll of 1" graph paper would be nice. I don't know the size of the grid, but I think you could find some cheap (garage sale?) wallpaper with a grid on the back- might be 1".

Sighting in 2 shots? Where's the fun in that? LOL. Not so easy to do when swapping scopes & the shots are going way off paper. I do like the method.

BTW, won the light class BR match today with the 7mm RM that prompted my original post. Had a little vertical stringing (downward as the barrel got hot). Comped for that a little, shot to shot. I was one of the RSO's and didn't shoot heavy. Helped a father & son to shoot my heavy AR since they had some trouble with the rifle they brought- I think one of them scored 2nd in heavy. Windham VEX AR is a tack drivin' son of a gun...

Very good..... it's nice when others shoot you gear and do well. I still need funds for a new optic. I just realized wife's Bday is upon me.....jeez where did Aug go?
I'm still waiting for some bullets also. Vendor said they shipped 6 weeks ago. Tracking number says it did but no other info after.... I got some 60 g r ain Sierra varmint bullets to try. Maybe they will do well in the 1/8 barrel?

 

[Mountain]

My Windham has a 1/8 barrel with a Compass Lake chamber. It 'likes' 69 grain and even 77 grain bullets. 60 would be better than 55...

 

[mac1911]

My Windham has a 1/8 barrel with a Compass Lake chamber. It 'likes' 69 grain and even 77 grain bullets. 60 would be better than 55...

I have not tried anything lighter than 69 match bullets so far other than some 55gn Hornady FMJ with some W844 surplus and surprise I get MOA with those?
I have yet to get better than a .75 moa group with any bullet/powder combo so far although testing is limited....

Still need to try the Amax through the "varmint/Bench" upper

 

[Stape]

What happened to bore sighting the old fashioned way? Remove the bolt, look through the bore, center the target in the bore and adjust scope...........

OP, glad it worked for you, that's awful impressive for a field rifle to shoot that good. What powder are you using? RL22? 4831?

 

[Mountain]

What happened to bore sighting the old fashioned way? Remove the bolt, look through the bore, center the target in the bore and adjust scope...........

OP, glad it worked for you, that's awful impressive for a field rifle to shoot that good. What powder are you using? RL22? 4831?

4831, 57 grains. CCI magnum primers (250?). Sorted brass, didn't really need to trim because length was uniform. Nothing special FC cases. Sorted the SMK's by length for groups of 5.

I installed a Timney trigger (and had to replace lost a washer I launched into orbit) but otherwise the rifle is stock- not bedded, not free floated. Stock trigger was pretty awful IMO.

If i get my match targets back, I'll post a pic of my vertical string. Horizontal displacement was nil. I used a little 'english' to make tiny POA adjustments for best group of .7-something today. In hindsight I could have used BR primers and the primer holes needed to be uniformed. A more accurate scale might help too. More overkill, but as mentioned good cheap fun with an old family rifle.

 

[mac1911]

What happened to bore sighting the old fashioned way? Remove the bolt, look through the bore, center the target in the bore and adjust scope...........

OP, glad it worked for you, that's awful impressive for a field rifle to shoot that good. What powder are you using? RL22? 4831?

Bore sighting is pretty good and gets you close. Although I find it just as easy to do this.

[video]https://m.youtube.com/#/watch?v=qwD5zu7yTeI[/video]

Plus it works on semi auto rifles.


Why won't videos show up ?