crimp and velocity

[vitaminado]

hello
I'm loading for a 338 wm.
I have to crimp because the bullets enter in the brass when they touch the magazine, due to the recoil.
brass: norma new
bullet: hornady sst 200 gr
primer: cci lr magnum
powder: vihtavuori n160
oal: cannelure bullet
medium-heavy crimp
loads:
-70gr: 2672 fps
-70.5: 2785 fps
-71: 2744 fps
-71.5: 2750 fps
-72: 2785 fps
-72.5: 2779 fps
according to the hornady manual, with 72.5 it should be around 2900 fps
What is the reason for the low velocity?
Can it be the crimp?
I put some pictures in case you see signs of pressure

 

[gohring3006]

It's not the crimp.
It's up to you if you want to go further in charge weight. From the looks of things, there is room to go further. But I'm looking at a pic, I'm not the one putting my face next to it when you pull the trigger.

 

[jjmp]

Pm sent , thks

 

[g0rd0]

Since the recoil is pushing the rifle back and slamming the bullets load the bullets touching the front of the mag.
it works for me in my Sav 111, 7mm rem mag and I never crimp.
BTW from your photos I see no flattening of the primers or no other signs of high preasure but, as stated above it is your face behind the bolt
As for the low vel. the people who are responsible (hornady speer hodgen, etal) have laboratories, and nothing but the best of equipment. Each rifle is unique and that same load in your brass from a different rifle will have similar and yet different results.
Wich is why most of us are chasing that donkey (to get the best reults we can)
Enjoy from the looks of things you are doing just fine

 

[jjmp]

Sent you a pm explaining ,no answer ,your no where near max pressure ! Own a 338 mag myself ,I don't crimp ever n never had a need to ! There's info out there , a good reloader should cross reference all powers with different reloading data from various sources , yes this is a forum so that's why I pmed you ,we all put our heads on the stock, but your loads are safe and under powered for a reason , but the question has been answered .

 

[Howland]

If anything, a firm crimp or stronger neck tension should increase pressure.

I wouldn't be concerned at all about velocity being 4% under predictions in the manual. Each rifle is different. Plus, you're using a different case and primer.

I don't see any signs of excessive pressure in the photos.

 

[vitaminado]

thanks for all the help received
I have been recharging for a short time and I have a lot to learn.
jjmp, sorry for not answering before, but now I have arrived home and I can answer.
I connected and read your messages but I can answer now
I apologize.
with hornady brass and 74gr , easily 3000 fps.without crimp.
I'm going to do the following tests.
what do you think?
-hornady brass with crimp
-new normas brass without crimp
-norma brass 1x with crimp

What has surprised me the most is that from 70 to 72.5 gr, the speed hardly changes
I think the cause will be the change of brass

 

[jjmp]

No apology needed ! 74.0 gns & Hornady brass 3000 fps is Very good Cronographing excellent all brass = diff internal volume know yur max charge by Cautionaly working up ! Sure experiment that way it's proofed by you nice smart !!!n/160 very good but not the fastest other great powders just saying ... Good yur bac reloading pm me any time np , regards n have fun bee safe !!!

 

[tim_w]

Crimping or specificly neck tension does effect pressure. Its effect on velocity can vary based on powder bullet combo others specs being the same. It changes the pressure curve. There is a larger build up of pressure in the chamber this has an effect of increasing the rate of powder burn. Peak chamber prezsure goes up but the pressjre curve shortens and bas a larger from peak and sharper drop off. In most cases crimps tends to increase ES and can negatively effect accuracy but in certain use cases its needed.

Your cases certainly do not show the laymans way of checking over pressure for the case. I can also tell you that primers condition, lack of sticky bolt, or ejector mark tell you nothing of where your peak chamber pressure is in relation to the SAAMI/CIP maximums. Way way too many variables. Spending some time with a piezo and strain gauge equip and some reference ammo will end those dillusions quickly.

As there is a known allowance of 10% variance for canister powder velocity adjusted for barrel length IME is the best ref without pressure testing equip. This off the manuals load data published maxs. Still going over is all on you. Ill never tell somone to do it with their gun.