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> Tikka T-3 chamber size and resizing
Tikka T-3 chamber size and resizing
@ 06:59 pm (GMT) |
Bert SaenenHiToday I've measured 45 once fired Lapua cases (fired with my Tikka T-3 in .308W). They were loaded to the maximum load (Wild Boar) for the bullet weight according to the Ramshot guide. The measurements (base to shoulder) were done with a Redding Instant Indicator and they are relative to the Redding supplied case gauge (minimum SAAMI dimension). These are the results: - 11 were 0.001” under SAAMI minimum - 27 were 0.002” under SAAMI minimum - 07 were 0.003” under SAAMI minimum - (my virgin Lapua cases are 0.003” under SAAMI minimum) This leads me to the following questions: 1) Does this mean that the chamber dimensions of my Tikka are near the SAAMI minimum or should I fire the cases once more to confirm this? 2) For sizing I use the Lee Collet Die for neck sizing and the Redding Body die for body sizing and shoulder set back (together with the Redding Competition shell holders). For setting up the Body die, what's the best practice? Should I use one of the tallest cases (minus 0.001”), set the shoulder back 0.001-0.002” and use that setting for all the cases? 3) In the past I had the strange situation that the base to shoulder case measurement grew after resizing. Could this be explained by a rather minimal chamber dimension and a sizing die that did not touch the case shoulder? The sizing of the case body would then push up the shoulder. Thanks. |
Replies
@ 07:41 pm (GMT) |
Nathan FosterRe: Tikka T-3 chamber size and resizingHi Bert,1. It sounds like the first loads used were very mild. The brass probably expanded, sealed the chamber wall, but then returned back to near its original dimensions. I do not think this is indicative of an undersized chamber, not at this stage. It could if anything be more of an indication that the max load you used is not reflective of what the max charge is for your individual rifle. This is most common if using a burn rate equivalent to Varget. 2. Is there actually a need to size the body of the case? Is chambering difficult if you don't size the body? From what you have described, I would guess that your once fired brass is very easy to chamber at this stage. 3. Regarding this particular die and its individual dimensions- the undersized body sizing die has extruded / lengthened the case during initial sizing which may also ruin concentricity from so much working. By the time you set back 2 thou, the entire case dimensions have been changed. This is discussed in detail in my reloading book. This question also leads us back to question 2. |
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@ 09:09 pm (GMT) |
Bert SaenenRe: Tikka T-3 chamber size and resizingHello Nathan, thank you for your reply.I have your reloading book, I will reread the chapter and see what I can find. About the loads used being mild, I don't know. Ramshot Wild Boar has indeed a similar burn rate to Varget. The loads used should give pressures over 61,000psi (should because I used sometimes similar bullet weights and types but not the same as in the guide). I have some velocity readings from that session (60cm barrel): 20x HDY 168gr AMAX, 46.2gr Wild Boar, COAL 2.800", AVG 2808fps 05x HDY 178gr BRHP, 44.9gr Wild Boar, COAL 2.800", AVG 2675pfs 05x LAPUA 155gr SCENAR, 47.5gr Wild Boar, COAL 2.810", AVG 2878fps 05x HDY 208gr AMAX, 42.1gr Wild Boar, COAL 2.810", AVG 2495fps These were certainly not hot loads but I don't know if I could qualify them as mild. In a next phase I am going to do some max pressure testing in 0.5gr increments with bullets seated at jam minus 0.020". Can I do this with virgin cases? If I remember correctly the growing cases were sized with my Forster FL sizer. At that time I didn't have a concentricity tool so I can't verify what the runout was with those cases... Now with the Lee Collet die and the Forster Micrometer seater, runout is well under control. About the body sizing. I have several reloading books, some authors advocate to FL size every time with factory chambers, others not. Based on what I had read, I was trying to get a minimal setback each reload to maintain consistency. I will reload a few with only neck sizing and fire them again and see what the base to shoulder measurement will be. |
@ 09:44 pm (GMT) |
Martin TaylorRe: Tikka T-3 chamber size and resizingBert can you reach the lands less .020 and maintain concentricty in a 308w?Other than the 208's there wouldn't be much left in the neck unless your Tikka has a really short throat. If you decide to full size set up your die by "feel", size one of the longer cases using Nathans instructions from his book. The case will grow when you under size, then slowly adjust the die down until you have the bolt feel that you like, ie just camming in. Size a few more and cycle them through the rifle, if happy lock up the die. Then worry about measurements if it helps you, but the die-chamber measurement "is what it is". Once the die is set, forget about it, job done! |
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@ 10:24 pm (GMT) |
Bert SaenenRe: Tikka T-3 chamber size and resizingHi Martin, thank you for your reply.When I did try this the first time I didn't have the concentricity tool yet. My main problem with seating this long was neck tension. Three of the four test cartridges (without primer or powder) collapsed in the Redding Instant Indicator. The one test cartridge I still have has minimal runout. The needle in the concentricity tool just wiggles a bit. FYI, these are the COAL and CBTO to jam I recorded (all with Lapua cases): Hornady 168gr AMAX: COAL 2.896" CBTO 2.274" Hornady 208gr AMAX: COAL 3.018" CBTO 2.281" Hornady 178gr HPBT: COAL 2.883" CBTO 2.273" Lapua 155gr SCENAR: COAL 2.944" CBTO 2.302" I don't know what this says about the throat of the Tikka. I got this procedure for load development from the AccurateShooter forums (posted by Erik Cortina in the "Long range load development at 100 yards" thread): find an accuracy node at jam minus 0.020", once you got the correct charge, test different seating depths from jam minus 0.010" to jam minus 0.040" in 0.03" increments. This sounded like a good procedure and that was what I was going to try. However, I ran into problems with the neck tension on the very long seated bullets... Will try it again, perhaps with an undersized mandrel in the Lee die. Otherwise I will have to seat the bullets deeper to start with. |
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@ 12:10 am (GMT) |
Nathan FosterRe: Tikka T-3 chamber size and resizingThat really is the wrong procedure for this cartridge design (seating to touch the lands). Gosh, this comes up again and again eh guys. Please see the COAL article in the accuracy section of this site or refer to my reloading book. |
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@ 12:31 am (GMT) |
Nathan FosterRe: Tikka T-3 chamber size and resizingTry not to over complicate things Bert. If you have my book, it will alllow you to make accurate loads without fuss. Try to keep it as simple as possible.If you missed the COAL instructions in the book, then you may have missed other factors too. If you can, please put all of these other thoughts and internal arguments over measurements you are having thanks to other authors out of your head (as Marty alluded to) and load the ammo. There is far too much intellectual bullshit in this game. Stephs job list this morning: Vacuum house. Make up 20 rounds sub half inch .308 ammo. Make up 20 rounds sub half inch .223 ammo crimped. Make up 10 rounds sub half inch .338 Edge ammo. Make lunch. Get Riley's dress ready for dance comps tomorrow. Dinner. My range finder will run of yards before her .338 ammo runs out of accuracy. If she can make accurate ammo while juggling all of these jobs, well, what can the rest of us do. |
@ 01:24 am (GMT) |
Warwick MarflittRe: Tikka T-3 chamber size and resizingBuy her some flowers Nathan! |
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@ 04:48 am (GMT) |
Martin TaylorRe: Tikka T-3 chamber size and resizingYep flowers are the go for sure! l wish l had help like that, never mind a bloody skilled hunting buddy as well.And yes, keeping things simple is what l was leaning towards, the 308W works as good as any other cal because it is so simple & efficient. Nathan told me something like "Max of 71mm coal, 2206H, find a node, fine tune powder & away you go" and it was that easy in both my 308's. They use the jump to gain some free velocity and it works very well. I love to mess around with them but the basics stay the same. |
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@ 06:11 pm (GMT) |
Bert SaenenRe: Tikka T-3 chamber size and resizingHello, thanks for your replies.@Nathan: I am not trying to seat to touch the lands (at least not intentionally). The measurements above are from the dummy rounds (method 2 in your book) to determine max COAL. I use them only as a reference point. Testing will be done at max COAL minus 20 thou (as in your rule of thumb for open tip match bullets). I have read about freebore issues with .308W in your book. I didn't know about that. The problem I had was with the dummies collapsing in the Redding Indicator. I will see what I can do about that. The actual reloads (at minus 20 thou) didn't have that problem. I will check for velocity ES and if it's too large I will seat the bullets deeper. The measurement records I keep are for quality control and safety and have proven useful to me. I can make reliable and (reasonably) consistent reloads to a given recipe in a short amount of time. What I am trying to do now is to learn how to develop a load and make a recipe of my own that will fit best with my rifle. This is a learning experience for me and I am ok with it if it takes some time. |
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@ 07:26 pm (GMT) |
Nathan FosterRe: Tikka T-3 chamber size and resizingBert, I did not give the advice you mentioned (20 thou jump) for the likes of the .308. There is section you have missed which from memory is just before that section.Would you be willing to try seating your ammo at 2.795", then experimenting from there? This will fit your mag and produce optimal performance with the bullets you are using. As long as the ammo is concentric, the case neck will guide the bullet to the bore squarely while also hopefully keeping ES low. Just remember, even if you can get your ammo concentric with 20 thou jump, some of those bullets will lose concentrity simply during handling. There is so little bullet in the case with the likes of the 168gr A-max at 20 thou and the ammo is easily bumped out of alignment. If you want to try long seating, try it with the 208gr bullet / single feeding. |
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@ 09:34 pm (GMT) |
Bert SaenenRe: Tikka T-3 chamber size and resizingHi Nathan, thanks for the explanation! Ah, I found the information you referenced in the article. Now I understand what you tried to explain to me. As I said , it is a learning experience for me. I will seat the 168gr AMAX to 2.975" COAL and use that as a baseline. So that when I get fancy ideas about seating depth, it should perform better than the baseline or be discarded... |
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@ 09:39 pm (GMT) |
Martin TaylorRe: Tikka T-3 chamber size and resizingI have read about freebore issues with .308W in your book. I didn't know about that.The freebore in 308W is not "an issue" that Nathan writes about, it is a fact and is built into every SAMMI spec rifle that l have seen Bert. An intentional design to gain velocity, just like in most Weatherby's and many other designs. As Nathan has said and you have questioned, ES and concentricity are largely controlled by the neck length/seating/tension which will be addressed by the deeper seating. Why seat so far out with short for calibre projectiles and compromise your loads in a design that just doesn’t need it to work very well? Is this used as a target rifle only? Work up your 71mm loads, job done, no need to fuss around and they will be robust, accurate, repeatable and feed through the mag! |
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@ 09:58 pm (GMT) |
Bert SaenenRe: Tikka T-3 chamber size and resizingHi Martin. I did not mean it that way. I am not a native English speaker so sometimes I miss the linguistic subtlety to correctly express what I want to say. What I meant was that it is something one certainly has to take into account and that I was not aware of it. I will try the 71mm seating depth. |
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