Odd noisy & slow shot in the middle of a string

Andy-shooter

Well-Known Member
Hi all, I’m looking for a bit of insight here...

Earlier this evening I reloaded a batch of 10 cartridges (.17 hornet) to speed test a load I had already confirmed as accurate. As I was running through all was going as expected then the 9th shot was significantly louder than the previous shots, the bullet hit the ground half way to the 100m target and the Chrono read 3300fps (vs 3750fps on the other shots).

i inspected the brass (nothing obvious) took the bolt out and checked for obstructions in the barrel, then checked the moderator for a strike (no problems) and then chambered and shot the 10th cartridge which was fine.

Any ideas what happened?

Andy
 

Andy-shooter

Well-Known Member
I suppose it could be that, I did weigh every charge and very carefully assemble them though.

I measured the brass last night and one was a bit over length. Unfortunately by that point I had mixed them up so I don’t know if it was shot 9 but now I am thinking maybe the slightly long brass got a very tight crimp on the bullet when I used the seating die (Hornady with roll crimp function)

The shot was earsplittingly loud even with a moderator so I suspend there was destination of the powder or a big pressure build somehow.
 

NigelM

Well-Known Member
I think you're probably on it Andy. I light load would not give you the extra loud bang. The noise is usually associated with more charge/pressure rather than less. You say you were very careful on the weighing and loading so we have to take you at your word.

If it wasn't a charge weight issue what would have caused more pressure but less velocity? Not sure a slight over crimp would have caused a velocity reduction of 450 fps - 14%. There would have been a greater pressure build up before the bullet exited the chamber which would have caused greater acceleration rather than less.

Primer issue? Perhaps very light ignition causing a delayed burn rate? What make were they? I'm guessing, but it's tough to work out what the problem is if you start from the position that the charge weight was correct.
 

Andy-shooter

Well-Known Member
I think you're probably on it Andy. I light load would not give you the extra loud bang. The noise is usually associated with more charge/pressure rather than less. You say you were very careful on the weighing and loading so we have to take you at your word.

If it wasn't a charge weight issue what would have caused more pressure but less velocity? Not sure a slight over crimp would have caused a velocity reduction of 450 fps - 14%. There would have been a greater pressure build up before the bullet exited the chamber which would have caused greater acceleration rather than less.

Primer issue? Perhaps very light ignition causing a delayed burn rate? What make were they? I'm guessing, but it's tough to work out what the problem is if you start from the position that the charge weight was correct.

The primers were Fiocchi, I have never had a problem with them before but... let’s assume a poor ignition, bullet blown out of the case with a load of unburnt powder, then powder ignites. That would I think cause a drop in velocity but a nasty bang - which is what I got.
 

NigelM

Well-Known Member
The primers were Fiocchi, I have never had a problem with them before but... let’s assume a poor ignition, bullet blown out of the case with a load of unburnt powder, then powder ignites. That would I think cause a drop in velocity but a nasty bang - which is what I got.

That's exactly where I got to.
 

Effnjeff

Well-Known Member
Which powder are you using?
I have found my 17 Hornet likes a medium crimp where the extra neck tension gives better groups and more consistent velocities. Crimping may eliminate your ignition problem too if it is that, but your initial description had me wondering if an accidental low charge had detonated.
 
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Andy-shooter

Well-Known Member
To add a bit more information to help with the puzzle, I reloaded 25 more of the same load, applied a light crimp to get consistent neck tension and then sent them down range.

All 25 were “normal” in terms of noise and showed fairly consistent velocity (3850-3900FPS) however they were wildly inaccurate.

At 100yds there was was no group whatsoever I couldn’t even reliably hit a piece of A4. I think the bullets were destabilising or breaking up in flight because at 25yrd there were grouping under an inch.

This has lead me to think the odd noisy shot from before may have tumbled in the moderator. I’ll strip it down tonight and inspect it.
 

Effnjeff

Well-Known Member
I haven’t used Lilgun, but I understand it peaks pressure easily in the 17 Hornet. I just checked my notes and I found that 10.2 grains of N110 was getting 3700fps with pressure signs and QL estimating max pressure.
I would guess that 3900fps could be well over pressure, albeit with a different powder.
Others have found that this bullet can hold together above 4000fps, but I had one fly apart inside my mod from my 17 Rem at that speed.
 

Andy-shooter

Well-Known Member
Thanks Guesty, no pressure signs on the primer and a smooth non-sticky bolt lift and extraction. I’m inclined to think these very frangible bullets are flying apart at that kind of speed.

More testing will follow.

If if I can keep them together until they hit a rabbit they should make an almighty mess of it.
 

soulboy1957

Well-Known Member
The ex hmr 17g bullets are not stable above 2900 Ish, I know they are cheap, but I only use 20g vmax now.
Had similar problems to you 2 years ago, I don't think they can take. 17 hornet speed.
 
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