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The ignition question

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Peter Armstrong Mk1
The ignition question

Guy

I thought it better to start a new thread on this.

There has always been a lot of talk about ignition but nobody seems to talk about what good ignition changes in the gun and it always easier to get from A to B if you know what B looks like so let’s talk about it.

If you tested a gun with average ignition over a chrono then fixed the ignition and touched nothing else, but the gun goes from average to a great shooter. You then go back and run the same tests over the chrono and the results are much the same. So the question is what has good ignition done to improve the gun??

Peter

BigStick
BigStick's picture
Well

Well I'll bite.
Kim

Dig
Dig's picture
Outcome

When this whole question was raised some weeks ago, I ran a test in the tunnel to see what changing the spring strength would yield in terms of performance. I guess I've always been an outcome focussed person and whilst a theory may provide a basis for a change, if the results don't support the theory then I guess I have come to believe the theory is flawed.
So I took 2 boxes of Eley Match (speed 1063) from the same batch. The first box I shot using my turbo 3 lug with the original spring which measured 8lb when compresses to 1 3/4".
Then I replace it with a new spring which measured 16lb at 1 3/4" and shot another 50 rounds.
As you would expect, the penetration results from the 16lb spring increased but only 003".
Results from the 8lb spring
Fastest speed 1084
Slowest speed 1048 (range 36)
SD 8.2fps
Average speed 1067
Median speed 1067 (which shows that the 50 shots were evenly distributed about the mean)
Group size 0.379"
Results for the 16lb spring
Fastest speed 1093
Slowest speed 1060 (range 33)
SD 8.1fps
Average speed 1075
Median speed 1074
Group size .366"
So with double the spring pressure the results are not statistically different from each other. What was surprising is that all the speeds of the second test increased by 8-12fps whilst the spread remained virtually the same. The group size reduced only 013" but the second group was slightly more round than the first.
What's it all prove?
I'm thinking if you have sufficient force to reliably ignite the primer, any more doesn't necessarily help. There could be a correlation however between the change in the group shape and the increase in the velocity but it would take far more data to reliably come to that conclusion.
Dig

Team KAOS - Lurking with intent
All the gear and "a bit more of an" idea

22 tech
22 tech's picture
surprising. fat post.

Surprising to see the speed change. Could you do a test with the spring at marginal force (low) as well.
Is some of ignition all about vibrations introduced because of hitting the case edge too hard or the stop?
Peter

Dig
Dig's picture
Bounce

When the bolt is closed, the distance between the bolt face and the chamber face is the headspace. Now this space is occupied by the cartridge rim which I find varies from 036"(Eley) to 039" (Lapua). Depending on the headspace there's a gap between the inside of the rim and the chamber face. When the firing pin strikes the rear of the case, the force applied attempts to move the case forward until the inside of the rim engages with the breech face. This movement however may be resisted by the projectile engagement into the lands. However at some point in the process this resistance is overcome and the case founds against the breech face allowing the firing pin to crush the rim.
So the actual ignition process is a function of firing pin force (controlled by spring pressure and pin movement resistance such as draging on the shroud), firing pin protrusion through the bolt face, headspace, rim thickness and chamber depth/leade angle(which controls the resistance).
So a simple thing like ignition is a little more complicated than first thought. Change any variable and you could see a change including a failure to fire.
I suspect if the headspace is small, the pin force excessive and the pin protrusion long, you are going to end up with bounce which itsnt good either.
Dig

Team KAOS - Lurking with intent
All the gear and "a bit more of an" idea

Robin
Groups

Thats a great group for 50 shots, or did you measure 5 individual 10 shot groups .

TheJet
TheJet's picture
Great question

As discussed on the other thread there are many things that effect good ignition.
Spring pressure is obviously one small part of them and as Digs has tested and explained on this thread.
But many other things were also brought up i.e. trigger timing,friction inside bolt, lug locking evenly etc

Not sure that all the answers to a great shooting rifle are contained in this subject though
Having the indent in the rim all be exactly the same says the total ignition is at least consistent which has been put forward by Bill Calfee as important
Has someone got some testing before and after that Bill has done anywhere as he does test his theories, seems to make sense as well.

So I put it to you Peter A what have you discovered about ignition in your many years of shooting?
You are one of Australia's most successful ever rimfire shooters, that is meant nothing other than the compliment that it is as it is a fact.
Barry Hillzinger always told me it was ammo - Barrel combination that made the most difference.
Micky T posed knowing when to shoot and when not to may be the most important.

I have no testing other than what I have shown though it seems I may have nearly made every mistake a man could make.
But I think ignition is important but only a piece of the puzzle.
Once you have that sorted then you can move onto the other factors that effect accuracy

Team KAOS
All the gear and no idea

Dig
Dig's picture
Group size

Robin
Each group was the entire 50 shots. The scope was adjusted so that the hole did not obilterate the aiming point.
It's not such a great group really as it is centre to centre. In the tunnel in Texas when we were testing ammo last year, our groups were a touch smaller and that was outside to outside, but that was TENEX however.
Dig

Team KAOS - Lurking with intent
All the gear and "a bit more of an" idea

Robin
Groups

Thanks dig , I've never shot 50 groups but i know there are times when a 5 shot group of that size would have been welcome .how did the 1067 -03 machine test , i still have some .

Dig
Dig's picture
1067-03

Not real good Robin. I have found 2 lots which shoot well. I'll bring you down a couple of boxes to Coffs for you to try.
The Tenex is doing 1078 through the chrono and the Match is just under at 1070. The good 332 we had was doing 1079 so they might just work in your rifle.
dig

Team KAOS - Lurking with intent
All the gear and "a bit more of an" idea

Robin
Groups

OK thanks ,kim and a couple of benchrest shooters hete at newcastle range purchased a number of test lots ,the batch that worked best for them was 03238 the next lot number after the one i gave you to test. The speed on box is 1080.

22 tech
22 tech's picture
Headspace, Engraving, Tip shape, Rim thickness

An interesting read http://castboolits.gunloads.com/showthread.php?11914-Primer-strike-force
I always thought people were using the inner portion of the firing pin strike to slow the pin so not to introduce vibrations due to bounce. It always puzzled me why the shape struck the inner of the case first as it would slow the pin before it had a chance to start ignition. Maybe its used to push the case forwards against the barrel face while a large spring force retains the speed for consistent primer ignition. Could explain why headspace, engraving & rim thickness make a difference. They all have to work together.
Will do the chrono test with weak verses strong strike before i let the pin shape be radically altered. As to Peter Armstong's original question if the speed doesn't alter but the rifle improves i don't know whats going on! Can you have more consistent barrel time with same chrono speeds?
Peter

TheJet
TheJet's picture
Speed of bullet

Not being a center fire shooter where you can load your own ammo each one exactly the same.
I have never really found the need to test the speed of ammo.
My test has been if they all land in the same place or not.

That being said I once helped out a very good shooter, recording the speeds that his bullets were going as he shot in a tunnel through a chrono.
It was actually quite interesting as the speed of the bullet made no difference at all to whether the bullet went high or low

Fast ones were sometimes going low ,slow ones were going high all over the place really and this was through his best rifle that had recently been tuned
He was looking for some ammo that would shoot at around the same speed but was not having a lot of success.
A different batch each target.

He must have shot ten different batches maybe on separate RBA cards
I wrote the speed down in another target I had at the bench and watched through the spotting scope to make sure I was writing it in the right target shot fifty meters away.

If there was a pattern showing it was certainly not apparent for speed of bullet and where it hit the target.

Team KAOS
All the gear and no idea

TheJet
TheJet's picture
whoops

whoops

Team KAOS
All the gear and no idea

BigStick
BigStick's picture
Peter Mk1

You asked the question and nothing since. Your not doing a Calfee on us are you.
I will be putting a reamer in a barrel soon. What is your ideal head space and engraving?
Dig, what if there is no space between the rim and the breech face so the bullet doesn't get pushed forward?
This is all theoretical and how will we ever know for sure? If NASA was into Rimfire then they would have an unlimited budget and it would be all sorted for us.
Then it would be up to us to read the wind, the most important part in my opinion.
Kim

Dig
Dig's picture
Less headspace

Kimbo
I'd be thinking if you reduced the headspace to zero, all the force required to engrave the projectile would be done by the caming action of the bolt. That would allow all the firing pin force to directed at crushing the rim.
And you are correct, at the end of the day no matter how good the ignition or the barrel/ammo combination, you've gotta be able to read the wind. Having said that of course, not having a gun that shoots consistently means you are behind the eight ball no matter how good you can read the wind.
We've on the way to skinny again. Fat people need not post.

Team KAOS - Lurking with intent
All the gear and "a bit more of an" idea

Peter Armstrong Mk1
Kim

Kim

When I started rimfire BR I quickly worked out that there are plenty of shooter out there with a lot more natural talent then me. So if I was going to get anywhere near the top I’d need to work harder and smarter than the others. One thing I did was doing 99% of my tuning and lot testing in the wind and one thing I found was ignition affects how well the gun shoots in the win.

Most people think that bad ignition means the speeds are all over the place and that’s why results on the target aren’t good, but it seem good or average ignition doesn’t seem to affect the spread of the speeds.

Good ignition gives you better combustion, so if better combustion doesn’t affect the spread of the bullet speeds what is it doing that is good for accuracy???

As far as chambers go, I don’t have a clue. I just pick a gunsmith that is getting good results and let him do his thing and I just concentrate on pulling the trigger at the right time. But none of my current match barrels are chambered with a reamer they were all done with boring bars.

Before someone tells my it is stupid to do all the testing in the wind, I’ll agree it is stupid. But the first 5 RBA nationals I shot the worst results was a 2nd place, the first group match I shot was nationals and I won the 50m agg, the first IRB and TRA nationals I shot I won. I was a bit slow with Hunter it was my 2nd nationals but I did shoot s 500. My point is all the barrels I used in those matches were all dialled in in the wind.

Peter

RBA HoF #1 (2007)

BigStick
BigStick's picture
Thanks

Thanks Mk1
If I can remember back that far, you were the first with a custom rifle and were streets ahead but the custom thing is catching up or is very common today and the scores are higher because the equipment is better. As Calfee says the first 95% is easy.
We are all chasing the last 5% and we all would like to be 100%. I think it is a great thing when your competitors get on and tell you and the rest of the world what things they did to improve
Kim

Dig
Dig's picture
Groups in the wind

Kim
I agree. By what the old folk tell me, the scores today are far more consitently better than they were a few years ago. I've only been in the game just on 4 years and have seen a huge improvement in that time. Sure there were some good scores shot in the "old days" but it's the consistency of those scores which has improved.

Peter also has a point about the wind. My tunnel testing is merely a way of choosing good ammo and a starting tune. My journey into centrfire has exposed me to other tuning processes and although they cannot be replicated with rimfire, the principle is the same however. I find that "good" ammo with give you a little more forgiveness in the wind. My rifle will also shoot tighter groups in a slight breeze than it will in a no wind condition. 2 years ago at Warwick, I shot in the first detail with no wind and a temp of about 3 degrees. In the first 2 rows of an IRB target I hit 1 dot before the wind came up just a little. I missed 2 dots in the remaining 3 rows.

Dig

Team KAOS - Lurking with intent
All the gear and "a bit more of an" idea

BigStick
BigStick's picture
Dig

I'd be thinking if you reduced the headspace to zero, all the force required to engrave the projectile would be done by the caming action of the bolt. That would allow all the firing pin force to directed at crushing the rim..
Good idea or not?
Why do /don't we have clearence. If the rim is 38 then why not 38 headspace?
The CF guys don't have space
Kim

Dig
Dig's picture
Clearance - headpace

In factory built rifles both rimfire and centrefire, clearances are always larger than "normally necessary" to allow for the use of different brands of ammo, each of which has it's own standard. They may or may not conform to the SAAMI std.
For custom built guns where the component tolerances are a lot tighter, the clearances could also be reduced.
Remember however, if you headspace yor rifle for 036"(Eley) you'll have trouble closing your bolt on a round of Centre-x. Might not close on any other brands either.
I believe you need some clearance otherwise any increase in the rim thickness(even within the same brand) will introduce differing pressure on the bolt nose.

Team KAOS - Lurking with intent
All the gear and "a bit more of an" idea

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