Velocity check

[OverInfinite]

Rifle: sig cross 6.5CM 18" barrel. Roughly 100 rounds through it with factory offerings and 50 berger 135 classics with a soft load of imr4350. Getting ready for a coues hunt so I started testing some different combos.
Brand new starline LR brass, chamfered and deburred, cci no. 200 primers same lot of 250 pieces.

Berger 140VLD Hunter with 42.3 H4350, loaded at max magazine length- 0.050" ish off the lands.
10 shot groups, 5 minutes between shots, using a gemtech tracker suppressor
AVG- 2722fps
SD- 12.4
ES- 34.3
Group- 1.18"

Hornady 143 ELDX with 42.0 H4350, loaded max magazine length- 0.040" off lands
Same series of fire
AVG- 2707fps
SD- 13.4
ES- 40.1
Group- 1.01"
I am very impressed. Brand new, not premium brass. Alot more speed then expected. Bo pressure signs at all. Great groups for hunting setup.
Am i crazy for thinking this is FAST for a 18" barrel?

 

[Andouille]

Yes, that is very fast and you are very likely running over pressure as your 143 ELD-X velocity is right at book load max for a 24" barrel. To confirm, you haven't seen ejector swipes, ejector marks, flattened primers, cratered primers, or a visibly apparent case head line at the base of the brass? Did you work up to this load, or just jump right to it?

Your velocity should be 135fps for 142gr bullet to 175ish fps 147gr bullet slower than published load velocities based on testing done by Rifleshooter.com. Assuming 140 fps loss, adjusted published load maximums are:
Hornady: 18" at 2,560 fps, 41.5gr H4350 vs 24" 2,700 fps
Hodgdon: 18" at 2,579 fps, 41.8gr H4350 vs 24" 2,719 fps

I'm currently loading for 20" 6.5CM tikka with 143 ELD-X, H4350, BR-2 primer, Lapua LRP brass and can lend some context from my observations. I'm getting 2,666fps at 41.9gr and 2,696fps at 42.2 gr with light pressure signs, and a measurable jump in case head expansion between the two. I'll load a couple at 42gr in Starline Brass to see if that brass results in higher pressure/velocity. I've noticed that Starline brass in my 30-06 doesn't readily show pressure signs at max loads.

Do you have access to a micrometer to measure and compare pre- vs post-fired case head diameter? An increase in diameter above the case web of 0.001 or greater seems indicative of high pressure based on my measurements and observations of Lapua brass.

Close-up, high resolution photos of your post-fired brass would be helpful.

 

[BCsteve]

Your velocities is your pressure sign.

 

[waspocrew]

You’re a bit fast. While I’m shooting factory ammo (so there’s probably some velocity left off the table), my 18” cross yields 2500 with 140 AAC black tip and 2640 with 127 LRX ammo.

 

[ztc92]

I agree with others, those velocities are quite high for a barrel that short and would worry me about pressure. For perspective, you’re getting the same velocities with those that I get with my 18” tikka hand loaded with 130 TMK and 130 ELDM.

 

[hoooogan]

Just shot a ladder of 142gr ABLR with H4350 with my 20" SA Redline yesterday. She was at 2743fps at 42.0gr and I was starting to see ejector markings. Your results are about on par with what -2" of barrel would have been with my load. For additional reference, I went one step further to 42.5gr and she spit out 2758fps.

 

[OverInfinite]

I know the velocities are high, that's what was concerning to me. I bought 40 rounds of hornady precision hunter ammo and it shot 2615 avg
When I load tested with the 140VLD I tested for pressure using 2 rounds each starting from 40.8gr and worked up to 42.4gr reusing the hornady 2nd time fired brass bumped 0.002" shoulder.
I have one piece of brass that showed the absolute slightest ejector mark at 42.0 gr but the other round showed nothing- chalked it up to maybe inconsistent neck tension or possibly chamber burr still working out.
I did the same thing with 143eldx. Ran from 41.2 to 42.4 gr h4350. No signs of pressure.

Switching to run starline I dropped 0.4gr and 0.5gr knowing, the brass capacity is possibly smaller and didnt want to run into issues. Then I loaded up the 2 groups of 10 using H4350 backed off a tad.

I didnt mind running up into the mid 42's since I have a couple other 6.5s that seem to like loads in the upper 41's. Both the ruger american, savage with a proof prefit and the ruger precision all have seen 42.4gr of h4350, 2 showed pressure signs. The precision never did.

 

[OverInfinite]

And here is the one piece of brass that showed an ejector mark.
Edit: brass shoulder growth is on average 0.003" on the brand new starline brass with this "hot" load. The starline brass is 0.001" short of what my comparator shows for the hornady brass after 2 firings.

 

[207North]

143 ELDX with 41.6 H4350 is getting me 2669FPS out of a 17” Bartlein. Yours seems in line.