Rifle reloading for accuracy

KDM · June 15, 2009, 10:22 PM

I've got a CZ 550 in 375 H&H. Want to "accurize" my loads by adjusting COL to fit the chamber. Starting off with Barnes 235 grain TSX flat base.

My chamber, as measured with a chamber length gauge, shows the 235 grain bullets touching the lands at around 3.8530". I thought I would shoot 5 rounds each at 3.600", 3.650", 3.700" and 3.750" and see which is most accurate. Powder charges would be "middle of the road" (76.5 grains of RL-15). Does this sound like a pretty reasonable course to take?

azredhawk44 · June 15, 2009, 10:31 PM

Not really, IMO.

You don't know if that middle of the road charge has the right explosive black magic mojo harmonics to be accurate in your rifle, anyways.

My understanding is to seat as long as you can, right to the point where the bullet ogive touches the lands. Find out what that length is. Then back down about 0.005 from there. Seating directly into the lands can cause overpressure, but if there is a few thousandths of freebore then there's no problem.

After that point, start tweaking your powder load. Usually peak accuracy is not going to be at max pressure. I don't own any rifle that takes a ~75gr charge (my biggest is a .450 Marlin), but I'd spitball and say to start around 70 grains. Looking at Alliant's page they list a Speer 235gr softpoint with a max charge of 78grains, so doing 5 each at 70/71/72/73/74/75/76 should get you some intriguing groups and cases to examine.

I'd be careful with an all copper bullet though. It's less dense and longer than a lead/copper bullet like the Speer this load data is for. It will take up more case volume that your load data assumes is not being consumed by bullet mass. I'd back off the max charge by at least 2 grains as a result.

IllinoisCoyoteHunter · June 15, 2009, 10:52 PM

+1. figure your powder charge/barrel harmonics first...then adjust your oal.

KDM · June 15, 2009, 11:16 PM

I hate good sound logic, AZ.

Thanks, guys. I'll give the advice a try.

Shoney · June 15, 2009, 11:18 PM

I generally start by determining the longest OAL that will fit in the magazine and still feed & function perfectly. Rule of thumb is to have at least one diameter length of the bullet in the neck for hunting bullets. Longer (less than one diameter) for target loads if you transport and hand feed them with care.

Because the 235 gr bullet is short in relation to the heavy bulllets for which the 375 was chambered to take, you may not be able to seat it very close to the lands.

Read this thread on finding "distance off the lands":
http://www.thefiringline.com/forums/...d.php?t=332789

butta9999 · June 16, 2009, 03:42 AM

I would not suggest seating your bullets so your kissing the lands. With such heavy bullets and slower burning powders you run the risk of high pressure spikes.

Lighter bullets and fast burning powder is a safer option, mainly in varmint rifles.

With heavy bullets and slower powder the pressure happens over a greater time. If the bullet is driven straight into the lands- rifling after firing the pressure will spike. A slight jump reduces this risk.

You have to take into account your shooting a .375 H&H not a .222, .204 looking for .25/.50 MOA at 100yds.

I would find a suitable seating depth taking into account the length of magazine then play with powder weights and brands. Even different primers will differ accuracy.

Another risk you have is lodging the bullet into the lands and when ejecting the bullet you will leave the lead in the barrel. Hence a heap of powder ending up in your action.

I am guessing this is for large possibly dangerous game, if so safe feeding rounds shooting MOA at 100yds is perfect.

Good luck in your achievements.

June 15, 2009, 10:22 PM	#1
KDM Senior Member Join Date: October 4, 2006 Location: California Posts: 457	Rifle reloading for accuracy I've got a CZ 550 in 375 H&H. Want to "accurize" my loads by adjusting COL to fit the chamber. Starting off with Barnes 235 grain TSX flat base. My chamber, as measured with a chamber length gauge, shows the 235 grain bullets touching the lands at around 3.8530". I thought I would shoot 5 rounds each at 3.600", 3.650", 3.700" and 3.750" and see which is most accurate. Powder charges would be "middle of the road" (76.5 grains of RL-15). Does this sound like a pretty reasonable course to take? __________________ "Ask not for a lighter load. Instead, ask for a stronger back."

June 15, 2009, 10:52 PM	#3
IllinoisCoyoteHunter Senior Member Join Date: December 23, 2008 Location: Southern Illinois Posts: 1,527	+1. figure your powder charge/barrel harmonics first...then adjust your oal. __________________ ~~IllinoisCoyoteHunter~~ ~NRA LIFE MEMBER~ ~NRA CERTIFIED INSTRUCTOR~

June 15, 2009, 11:16 PM	#4
KDM Senior Member Join Date: October 4, 2006 Location: California Posts: 457	I hate good sound logic, AZ. Thanks, guys. I'll give the advice a try. __________________ "Ask not for a lighter load. Instead, ask for a stronger back."

June 15, 2009, 11:18 PM	#5
Shoney Senior Member Join Date: February 21, 2002 Location: Transplanted from Montana Posts: 2,311	I generally start by determining the longest OAL that will fit in the magazine and still feed & function perfectly. Rule of thumb is to have at least one diameter length of the bullet in the neck for hunting bullets. Longer (less than one diameter) for target loads if you transport and hand feed them with care. Because the 235 gr bullet is short in relation to the heavy bulllets for which the 375 was chambered to take, you may not be able to seat it very close to the lands. Read this thread on finding "distance off the lands": http://www.thefiringline.com/forums/...d.php?t=332789 __________________ I pledge allegiance to the Flag - - -, and to the Republic for which it stands….Our Forefathers were brilliant for giving us a Republic, not a democracy! Do you know the difference??? and WHY?http://www.wallbuilders.com/LIBissue...les.asp?id=111

June 16, 2009, 03:42 AM	#6
butta9999 Senior Member Join Date: June 29, 2008 Location: Melbourne, Victoria, Australia Posts: 692	I would not suggest seating your bullets so your kissing the lands. With such heavy bullets and slower burning powders you run the risk of high pressure spikes. Lighter bullets and fast burning powder is a safer option, mainly in varmint rifles. With heavy bullets and slower powder the pressure happens over a greater time. If the bullet is driven straight into the lands- rifling after firing the pressure will spike. A slight jump reduces this risk. You have to take into account your shooting a .375 H&H not a .222, .204 looking for .25/.50 MOA at 100yds. I would find a suitable seating depth taking into account the length of magazine then play with powder weights and brands. Even different primers will differ accuracy. Another risk you have is lodging the bullet into the lands and when ejecting the bullet you will leave the lead in the barrel. Hence a heap of powder ending up in your action. I am guessing this is for large possibly dangerous game, if so safe feeding rounds shooting MOA at 100yds is perfect. Good luck in your achievements. __________________ Knowledge is Power!

June 15, 2009, 10:31 PM	#2
azredhawk44 Junior member Join Date: September 28, 2005 Location: Mesa, AZ Posts: 6,465	Not really, IMO. You don't know if that middle of the road charge has the right explosive black magic mojo harmonics to be accurate in your rifle, anyways. My understanding is to seat as long as you can, right to the point where the bullet ogive touches the lands. Find out what that length is. Then back down about 0.005 from there. Seating directly into the lands can cause overpressure, but if there is a few thousandths of freebore then there's no problem. After that point, start tweaking your powder load. Usually peak accuracy is not going to be at max pressure. I don't own any rifle that takes a ~75gr charge (my biggest is a .450 Marlin), but I'd spitball and say to start around 70 grains. Looking at Alliant's page they list a Speer 235gr softpoint with a max charge of 78grains, so doing 5 each at 70/71/72/73/74/75/76 should get you some intriguing groups and cases to examine. I'd be careful with an all copper bullet though. It's less dense and longer than a lead/copper bullet like the Speer this load data is for. It will take up more case volume that your load data assumes is not being consumed by bullet mass. I'd back off the max charge by at least 2 grains as a result.