COL, do I match the book or factory load?

[smbaas]

I am working up a new load for my 7mm Rem Mag and am wondering if I made a mistake on where to start out with the COL. I figured I would be safe mirroring factory Remington premier accutip ammunition COL, which was 3.237. Also when I compare the amount of the cantalour on the bullet that I can see when seated it looks correct according to my reloading books and the Remington premier accutip ammunition.

But as I am looking through many of the posts here, yes I used the search function before I posted this, I am seeing that most posts COL for 7mm Rem Mags are around 3.280 - 3.290. I have read and think I understand that the COL that is best for your rifle is based on how far from where the bullet starts to impact the rifling, and that seating the bullets that impact the rifling upon chambering can greatly increase pressure. But what about the other way around?

So my question is, am I safe with the below loads COL or do I need to pull them and go based off the Hornady reloading manual COL which is 3.250 for 139gr and 3.290 for 154gr? Below are the loads I am referring to.

Ammunition Type: 7mm Rem. Mag.
Bullet: Hornady 154 gr SST
Case trim length: 2.491
Powder: RL-25
Powder Gr. 65.1
COL 3.24

Ammunition Type: 7mm Rem. Mag.
Bullet: Hornady 139 gr SST
Case trim length: 2.491
Powder: RL-25
Powder Gr. 69.5
COL 3.228

Thanks for your advise on a newbie reloading question!

 

[Ol` Joe]

3.290" is the max COL that will fit in any SAAMI magazine, it has nothing to do with the throat. I`d load either to the COL used by the manual developers or determin the distance to the lead of your rifles throat and load just off that or shorter.

 

[NCsmitty]

smbaas, your loads should be fine at the COAL that you have now. You can play around some with the COAL when you reload the next batch. You need to reach a balance in allowing the rounds to fit the magazine, without jamming the bullets into the rifling.
IMO, your powder charge is low enough to be safe. If you move the bullets out, you may need to add more powder because your powder space in the case increases and will likely reduce the chamber pressure and velocity, if you use the same charge.
I believe Alliant lists 70gr of Rel-25 as the MAX load with 160gr SP on their site.
Work to achieve the balance of accuracy and velocity that satisfies you.


NCsmitty

 

[smbaas]

Thanks for looking over all that info! I feel much better now heading to the range to try them out. I will also plan on picking up an OAL gauge so I am not guessing quite so much.

 

[rfwobbly]

I will also plan on picking up an OAL gauge so I am not guessing quite so much.

OAL is not something you want to guess at for reasons of safety and best accuracy. With that in mind, the best instrument to have is a digital caliper. This will let you measure the length (OAL) of any cartridge with authority. Many reloading vendors sell them, but you might try "Harbor Freight" first. They have a nice set that goes on sale about twice a year which reads in inch & mm for $13.

If you already have the caliper, then you surely don't need an OAL gauge. A much better buy might be a cylindrical cartridge gauge. This would mimic the chamber and check the roundness, size and lengths of several features in one easy measurement.

Hope this helps!

 

[interlock]

Col for duffers

GUYS I ORIGINALLY POSTED THIS ON SD. A UK FORUM, THERE IS A SECTION IN THIS ABOUT GETTING YOUR COL CORRECT. THERE IS A LOAD MORE WHICH I CAN POST IF REQUIRED

Ok guys here we go. time to look at reloading.

my situation. i live in lincolnshire. i shoot mainly roe deer but sometimes bigger deer. i shoot over big fields quite a lot and the range is sometimes quite long. so i need to deliver a bullet which will kill all uk deer at quite long ranges (stalking speaking). i have a 7mm08 which i shoot 139's out of so i don't want to duplicate my loads, it is not a very accurate rifle so it is not really suitable for this.

I have a parker hale .30-06 model 1200. it has a 24 inch barrel and is very accurate. this will be the tool for the job. Which bullet shall i use? the rifle is capable of firing bullets from 110 gr to 220+ but what will be best. I will find out the twist rate.



i make a small mark on my cleaning rod near the rotating handle. and put a tight fitting patch on the jag,



i push it in until it is well in the rifling and the mark is near my thumb. ai then mark the rod where it goes into the breech.

i push it in until the mark appear again near my thumb, one full turn. then mark the rod again where it goes into the breach.



i measure the gap and it is 9.75 inches long.
so my rifle has a twist rate if 1:9.75 (ish). i come into the house and do a bit of surfing. checking out this site, this sites archives, the high road and reladers nest. This tells me that this twist rate is really quite fast for a .30-06 and is ideal for heavier bullets. so i look about and see what i can find in relation to velocities, ballistic coefficients and styles. i use hornadies ballistic calculator (amongst others) to see what i like the look of best. I find that a 165gr boat tail bullet is good for 3000 fps and has a really flat trajectory.

i like the soft point bullets not the ballistic tips (personal preferance only). so i give midway a quick check and find they have 165spbt bullets on offer R E S U L T.!



So i buy 200 (about 3 months ago) and they sit on the shelf. my life has been a bit upside down.

now i have a quick surf on the hodgdon site and look at what they say about powders. thier testing is with a 24 inch test barrell (same as mine) and they give IMR4350 as the best performer with 165gr with 60 gr compressed load it says 2934. I remember reading 63gr on another site but i can't find it so i will stick with hodgdon data. The Imr4350 is a slow burning powderso in a big 30-06 case it will be the ticket to push that bullet out of the long barrel

so next i need to get the oal length checked. the ogive is different on these than the stubby little 150 gr.
starting with a full length resized case, trimmed to length. (details on how to do this will follow).



set your seating die up so that it is slightly not touching the ram. this is important. if you make them touch you will get a taper crimp on your rounds which in my opinion isn't needed.

unscrew the seating depth adjuster a long way



seat your bullet very long but so it will fit in your magazine



colour the bullet with a marker pen



load it into the rifle from the magazine if you have a forced feed rifle like a mauser. go steady as you cam the bolt over, any resistance means the bullet is too long. it maybe it gets stuck in the rifling and you need to push it out



don't worry about this, it's ok if the soft bit is slightly deformed. it doesn't touch the rifling and the seating dies normally have quite a wide cup.

if the round comes out ok, check the bullet for little marks at equal intervals around the bullet. this is where the rifling has touched.



keep turning the seating depth down half a turn at a time until this stops happening and the bullet comes out ok. the pen is not disturbed.



lock down your depth. this is ok for a start point. (i know some of the more technical guys will think you need gauges, and to be fair, to get the best results you do)

next step is to resize your brass and de prime. there are different ways to do this, some only necksize, it increases your brass life. i full length because i don't have nexk sizing stuff. brass prep is really important and you can do a lot on it.

 

[Ol` Joe]

dyeing the bullet and chambering watching for marks in the ink works to get you a baseline as to where the lands are with that bullet only, change brand or style of bullet and you have to do it all over again.

I also wouldn`t give up on the 708 for your deer. I use 120 gr ballisitic Tips on them here at ~3000fps from my M700 and accuracy is better then any 129- 140 gr bullet I`ve shot from the rifle, and the bullet is as tought a piece of metel as you`d want. Most of my shots are right off the muzzle of the rifle in the swamps I hunt but I would not have any problem with useing it out to 400-450 yds on game.
I`ve talked to hunters on some of the boards that use this combo (120 BT in a 708) or the 280 AI with the 120 BT on game up through elk. This bullet uses the 140 gr BT jacket with the tip cut off to shorten it to proper lgt for its weight, this makes for one very tough bullet that still expands well. You might want to look at them further.
This isn`t knocking the 139 gr Hornady SP as a deer bullet. I`ve shot a few deer with them and they perform very well. I truely believe they are one of the better bullets out there for cartridges that run them around 28-2900 fps or less. They simply have been replaced in my loads lately by one I believe will prove to do better.

 

[interlock]

ol'joe,
Thanks for this. I really have no intention of not using my 7mm08 for deer. thanks for the advice about bullets. I asked the other day about ballistic silver tip specifically for this rifle. I have successfully culled deer using 120 gr prohunter 130 gr speer hot cor and 145 gr speer hot cor. I am a pretty experienced hunter culling up of 50 animals a year. It's just that THR is the biggest forum i am a part of and you american guys have better access to componants.

The above section of an article was to give the OP a guide to how to achieve a good oal for that particular combination of componants.

Interlock

 

[ranger335v]

"COL, do I match the book or factory load?"

Yep.

Or, better yet, find what actually shoots best in your rifle.